Electromagnetic Induction: The phenomenon of producing an induced electric current in a coil (or conductor) due to a changing magnetic field (or relative motion between a coil and a magnet) is called electromagnetic induction.

Observation: When a strong bar magnet is held stationary near one end of a coil, the galvanometer shows no deflection.

Justification: Electromagnetic induction occurs only when there is a change in the magnetic flux linked with the coil. When the magnet is stationary, the magnetic flux through the coil remains constant — it does not change with time. Since there is no change in flux, no EMF is induced in the coil, no current flows, and hence the galvanometer needle remains at zero.

Source: Chapter 13 — Magnetic Effects of Electric Current (Electromagnetic Induction section)

---

• Examiners expect the definition clearly stated (1 mark), the correct observation — no deflection — stated explicitly (1 mark), and a reason based on the concept of changing flux (2 marks).
• A common mistake is writing "the galvanometer deflects" — remember, only a moving or changing magnet induces current. Stationary magnet = no change in flux = no induced current.
• The key phrase to use: "no change in magnetic flux."

(a) A galvanometer is used because it can detect very small currents. When the magnet moves towards the coil, the magnetic flux through the coil changes, inducing an EMF and a momentary current — causing the needle to deflect. The deflection is momentary because current is induced only while flux is changing.

(b) No deflection would be observed. When coil and magnet move with the same speed in the same direction, there is no relative motion between them, so magnetic flux does not change and no EMF is induced.

(c) Conclusion: A changing magnetic flux (relative motion between magnet and coil) induces an electric current — this is electromagnetic induction.
Yes, deflection increases — more turns increase the flux linkage and a stronger magnet produces greater flux change, both resulting in higher induced EMF and larger deflection.

Source: Chapter – Magnetic Effects of Electric Current (Electromagnetic Induction activity)

---

• Examiner expects the term relative motion in (b) — this is the key justification.
• For (c), two sub-points are expected: the conclusion (electromagnetic induction) and the effect of more turns + stronger magnet (more deflection). Don't miss either.
• "Momentary" deflection must be explained by flux changing only while motion occurs — steady flux = no current.

Magnetic field lines of a bar magnet prove this as follows:

• Direction: By convention, field lines emerge from the north pole and merge at the south pole (outside the magnet), and run from south to north inside it. The direction of the field at any point is the direction a free north pole would move there.

• Magnitude: Where field lines are crowded (near the poles), the field is stronger; where they are spread apart, the field is weaker.

Since field lines show both direction and magnitude, magnetic field is proved to be a vector quantity.

Source: Chapter 12, Section 12.1 — Magnetic Field and Field Lines

---

Examiners expect two distinct points: one linking field-line direction to the direction of the field, and one linking crowding/spacing of field lines to the magnitude/strength. Mentioning "vector quantity" as the conclusion is a bonus but keeps the answer crisp. Avoid lengthy descriptions of the bar-magnet diagram; just state the two properties directly.

(a) When current flows from B to A with the magnetic field directed vertically upward, applying Fleming's Left-Hand Rule, the rod is displaced towards the left. This is because a force acts on the current-carrying conductor perpendicular to both the current and the magnetic field.

(b) When rod AB is aligned parallel to the magnetic field and current is passed, no displacement (no force) is observed. This is because the force on a current-carrying conductor is maximum only when current and magnetic field are perpendicular to each other; when they are parallel, the force becomes zero.

Source: Chapter 12, Section 12.3 — Force on a Current-Carrying Conductor in a Magnetic Field

---

• For (a), the key phrase is Fleming's Left-Hand Rule: field upward, current B→A (horizontal) → force toward the left. The textbook Activity 12.7 directly states the rod displaces left.
• For (b), examiners expect you to state no force/no displacement and give the reason: force is zero when current is parallel to the field (angle = 0°). The textbook states displacement is largest when current is at right angles to the field, implying zero when parallel.
• Always name Fleming's Left-Hand Rule for part (a) — it fetches marks.

(c)

Diagram:

```
↑ (Current flowing upward, out of page at top)
|
← ← | → →
↖ | ↗
← ← • → → • = current coming OUT of page
↙ | ↘
← ← | → →
|
```

The magnetic field lines around a current-carrying straight conductor are concentric circles centred on the conductor.

• The conductor is held vertically; current flows upward (indicated by arrow ↑).
• The magnetic field lines are closed concentric circles in the horizontal plane around the conductor.
• Direction of field lines is determined by the Right-Hand Thumb Rule: wrap the right hand around the conductor with thumb pointing in the direction of current — the curled fingers give the direction of field lines (anticlockwise when current comes towards you).
• Field lines are closer near the conductor (stronger field) and farther apart away from it (weaker field).

Source: Chapter 13 – Magnetic Effects of Electric Current, Oersted's Experiment / Magnetic Field due to Current in Straight Wire

---

Examiners award marks for: (1) a clear diagram with concentric circles, (2) arrow on the conductor showing current direction, (3) arrows on field lines showing correct direction (anticlockwise for current towards viewer), and (4) mention of Right-Hand Thumb Rule. Make sure the diagram is neat and labelled — roughly 2 marks are for the diagram and 2 for the written explanation/rule.

(a) When current flows through conductor AB, it experiences a mechanical force due to the interaction between the current-carrying conductor and the magnetic field of the horseshoe magnet. This force causes the rod to get displaced.

(b) Fleming's Left-Hand Rule — Stretch the thumb, forefinger, and middle finger of the left hand mutually perpendicular. If the forefinger points in the direction of the magnetic field and the middle finger in the direction of current, then the thumb points in the direction of force on the conductor.

(c)
(i) Using Fleming's Left-Hand Rule: magnetic field points from N to S (vertically, say downward), current flows from B (North) to A (South), i.e., southward. The rod will be displaced towards East.

(ii) Electric motor and Loudspeaker (moving-coil)

Source: Chapter 13 – Magnetic Effects of Electric Current, NCERT Class 10 Science

---

• (a) The key concept is force on a current-carrying conductor in a magnetic field — always state both factors (current + magnetic field = force).
• (b) Examiners expect the full statement of Fleming's Left-Hand Rule, not just the name. Name + rule = full marks.
• (c)(i) Apply the rule carefully: N pole is at bottom → field goes upward (N→S inside magnet = bottom to top); current B→A = North to South. Using FLHR: field ↑, current direction South → force acts East (or West depending on exact orientation — apply rule consistently). Examiners look for correct application of the rule.
• (c)(ii) Any two valid devices are acceptable: electric motor, electric bell, loudspeaker, galvanometer.

(i) Maximum Force:
The force on a current-carrying conductor placed in a uniform magnetic field is maximum when the direction of current is perpendicular (at right angles) to the direction of the magnetic field.

(ii) Minimum Force:
The force is minimum (zero) when the direction of current is parallel to the direction of the magnetic field.

Source: Chapter 12, Section 12.3

---

• Examiners expect the key condition stated clearly: 90° → maximum force; 0° (parallel) → minimum/zero force.
• The textbook explicitly states: "the displacement of the rod is largest when the direction of current is at right angles to the direction of the magnetic field."
• For minimum, if current and field are parallel, no force acts — this is the logical counterpart and standard expected answer.
• Use the words "perpendicular" and "parallel" — vague answers lose marks.

(a) In figure 'a', the field lines emerge outward from the facing ends, indicating both P and Q are North poles.

In figure 'b', field lines emerge from R and merge into S, so R is North pole and S is South pole.

(b) The magnetic field lines emerge from the North pole and merge (enter) at the South pole outside the magnet. Inside the magnet, they travel from South pole to North pole. Thus, magnetic field lines are closed curves.

Source: Chapter 12, Section 12.1 – Magnetic Field and Field Lines

---

• Examiners look for correct pole identification based on direction of field lines (emerging = North, entering = South).
• In figure 'a', both inner ends repel field lines outward → both are North poles (like poles facing each other).
• The key inference the textbook states: field lines are closed curves — always mention this for inference-based questions.
• Part (a) carries 2 marks (½+½+1), so name all four poles clearly.

Solenoid: A coil of many circular turns of insulated copper wire wrapped closely in the shape of a cylinder is called a solenoid.

When it behaves as a magnet: When electric current flows through a solenoid, one end behaves as a north pole and the other as a south pole, just like a bar magnet.

Diagram:

```
N |————————————————————| S
→ → → → → → →
→ → → → → → →
→ → → → → → →
```
(Field lines inside are parallel and straight, indicating a uniform magnetic field directed from S-pole end to N-pole end inside the solenoid.)

Source: Chapter 12, Section 12.2.4

---

• Definition (1 mark): Must mention "many circular turns," "insulated copper wire," and "cylindrical shape."
• Condition (1 mark): Current must flow through it; one end = N pole, other = S pole.
• Diagram (1 mark): Show parallel, equally spaced, straight field lines inside pointing from south to north end (inside the solenoid). Examiners check that lines are parallel and the direction is marked. Even a neat sketch with arrows scores full marks.

(a) Right-Hand Thumb Rule: Imagine holding the current-carrying straight conductor in your right hand with the thumb pointing in the direction of current. The fingers wrapping around the conductor give the direction of the magnetic field.

(b) Fleming's Left-Hand Rule: Stretch the thumb, forefinger, and middle finger of the left hand mutually perpendicular. If the forefinger points in the direction of the magnetic field and the middle finger in the direction of current, the thumb points in the direction of force on the conductor.

Source: Chapter 12, Sections 12.2.2 and 12.3

---

• Two distinct rules are being asked — one per sub-part, so label them clearly.
• Examiners look for the name of the rule plus a correct brief description of finger/thumb positions.
• A common mistake is confusing the right hand (for magnetic field direction) with the left hand (for force direction) — remember: Right-hand for fiReld, Left-hand for force (Lorentz/motor).
• You don't need a diagram in a 2-mark answer, but correct finger assignments are essential.

(d) is same at all points.

The field lines inside a solenoid are parallel straight lines, indicating a uniform magnetic field at all points inside it.

Source: Chapter 12, Section 12.2.4 – Magnetic Field due to a Current in a Solenoid

The passage explicitly states: "The field lines inside the solenoid are in the form of parallel straight lines. This indicates that the magnetic field is the same at all points inside the solenoid." Examiners expect you to select option (d) and may ask for a one-line justification — always mention "uniform" or "same at all points."

(i) Magnetic field line patterns:

Solenoid: Field lines inside are parallel and straight (uniform field); outside they emerge from one end and re-enter the other, similar to a bar magnet pattern.

Bar Magnet: Field lines emerge from the North pole, curve around, and enter the South pole; inside the magnet, lines run from South to North. All lines are closed curves.

(Diagrams should show these patterns with arrows indicating direction.)

(ii) Two distinguishing features:

1. The magnetic field of a solenoid is produced by electric current and can be switched on/off, whereas a bar magnet's field is permanent and always present.
2. The strength of a solenoid's field can be varied by changing the current, but the bar magnet's field strength cannot be easily changed.

---

• Examiners expect recognisable labelled diagrams for (i) — draw clearly with arrows showing field direction (N→S outside, S→N inside).
• For distinguishing features, focus on origin of field (current vs. permanent magnetism) and controllability — these are the most scoring points.
• Both diagrams carry ~1 mark together; the two features carry 1 mark each. Keep the answer concise.

(i) The rule used to find the force on a current-carrying conductor in a magnetic field is Fleming's Left-Hand Rule. Stretch the thumb, forefinger, and middle finger of the left hand mutually perpendicular. If the forefinger points in the direction of the magnetic field and the middle finger in the direction of current, then the thumb points in the direction of force on the conductor.

(ii)

• (1) Maximum force → Diagram (i) (electron moving vertically upward, perpendicular to the field).

Reason: Force is maximum when the charged particle moves perpendicular to the magnetic field (angle = 90°).

• (2) Minimum (zero) force → Diagram (iii) (electron moving parallel to the field).

Reason: Force is minimum (zero) when the particle moves parallel to the magnetic field (angle = 0°).

Source: Chapter 12, Section 12.3 — Force on a Current-Carrying Conductor in a Magnetic Field

---

• Examiners award 1 mark for naming Fleming's Left-Hand Rule and briefly stating it.
• For part (ii), identify the correct diagrams AND give the reason based on angle between velocity and field — this is the key concept. Maximum force at 90°, zero force at 0° (parallel). Diagram (ii) is the intermediate case, so it is neither max nor min.
• Note: for an electron, current direction is opposite to its motion, but the angle-based reasoning for magnitude of force remains the same.

(a) Both (A) and (R) are true and (R) is the correct explanation of (A).

The field is n times larger with n turns because current in each turn flows in the same direction, so magnetic fields due to each turn add up.

The source passage (12.2.3) directly states: "if there is a circular coil having n turns, the field produced is n times as large… because the current in each circular turn has the same direction, and the field due to each turn then just adds up." This makes (R) the precise reason for (A), so option (a) is correct.

(c) zero

By the right-hand thumb rule, the magnetic field due to the upper wire at P is directed out of the page, and the field due to the lower wire at P is directed into the page. Since both currents are equal and P is equidistant, the two fields are equal in magnitude but opposite in direction, giving a resultant of zero.

For two parallel wires carrying current in the same direction, apply the right-hand thumb rule to each wire separately at point P (midway between them). The field from the upper wire curves downward at P (into the page on one side), while the field from the lower wire curves upward at P (out of the page on the same side) — they cancel exactly. This is why the answer is (c) zero. Had the currents been in opposite directions, the fields would add up instead of cancelling.

Device used: Solenoid (a coil of insulated copper wire carrying electric current).

Diagram:

```
Battery (B)
+---|===|---+
| |
| S N |
====|============|==== ← Solenoid coil
| [soft iron cylinder inside]
| |
+-----------+
Switch (K)
```

A soft iron cylinder is placed inside a current-carrying solenoid. The strong uniform magnetic field inside the solenoid magnetises the soft iron, forming an electromagnet.

Source: Chapter 12, Section 12.2.4

---

• The key device is a solenoid connected to a battery.
• The diagram must show: the solenoid coil, soft iron core inside, battery, and switch — all labelled. Examiners award 1 mark for naming the device and 1 mark for the correct labelled diagram.
• Remember: the magnetic field inside a solenoid is uniform, which is why it effectively magnetises the material placed inside it.

Diagram:

```
↑ (Current flowing upward)
|
← ——|—— →
( ) | ( ) ← Concentric circles (magnetic field lines)
→ ——|—— ←
|
```

A straight conductor carrying current upward produces concentric circular magnetic field lines around it. By the right-hand thumb rule, if the thumb points in the direction of current, the curled fingers show the direction of magnetic field lines (anticlockwise when viewed from top, for upward current).

Source: Chapter 12, Section 12.2.1 & 12.2.2

---

• Examiners expect a neat diagram showing the conductor as a straight vertical line with concentric circles around it, arrows on circles showing field direction, and an arrow on the conductor showing current direction.
• Label at least: current direction (↑), magnetic field lines (concentric circles with arrows).
• Mention of right-hand thumb rule for direction earns the second mark.
• The key fact: field lines are circles centred on the wire, not straight lines — this is a common MCQ trap too (Exercise Q1, answer d).

Diagram:

```
↑ (current upward, marked with dot •)

← ⊙ →
(anti-clockwise concentric circles)
```

The magnetic field lines form concentric circles around the conductor, directed anti-clockwise when current flows vertically upward (out of the page, shown by ⊙).

(i) Direction of current: upward / out of the page (⊙)
(ii) Magnetic field lines: concentric circles, anti-clockwise

Right-Hand Thumb Rule: If a current-carrying straight conductor is held in the right hand such that the thumb points in the direction of current, then the curled fingers show the direction of magnetic field lines around the conductor.

Verification: With the thumb pointing upward (current direction), the fingers curl anti-clockwise — this matches the directions marked in the diagram. Hence, the directions are in accordance with the right-hand thumb rule.

Source: Chapter 12, Section 12.2.2

---

• The diagram must show ⊙ (dot) at the centre to indicate current coming out/upward, and concentric circles going anti-clockwise.
• Examiners award 1 mark for the correct diagram, 1 mark for stating the rule correctly, and 1 mark for the verification.
• The key phrase in the rule is: "thumb → current direction; curled fingers → field direction."
• Do not confuse anti-clockwise (current upward) with clockwise (current downward).

(D) (A) is false, but (R) is true.

The Assertion is false — increasing current increases the deflection of the compass needle, not decreases it. The Reason is true — magnetic field strength increases with increasing current.

Examiners expect you to identify that the Assertion directly contradicts what Oersted's experiment shows: greater current → stronger magnetic field → greater deflection of the needle. The Reason is a correct statement of the principle. Option (D) is the only choice where R is true and A is false.

(B) direction of the current flowing through it

The strength (magnitude) of the magnetic field of a solenoid depends on the number of turns, current magnitude, and core material — but NOT on the direction of current, which only affects the polarity, not the strength.

• The question tests the difference between strength (magnitude) and direction of the magnetic field.
• Changing current direction reverses the poles (north↔south) but does not change the magnitude of the field.
• Number of turns, current magnitude, and core material (e.g., soft iron core increases field strength) all affect the strength.
• Option (C) "radius of solenoid" is a slight distractor — for an ideal solenoid the field inside is largely independent of radius, but the syllabus-level answer the examiner expects is (B).

(i) Right-Hand Thumb Rule:
Imagine holding a current-carrying straight conductor in your right hand such that the thumb points in the direction of current. Then the fingers wrapping around the conductor indicate the direction of the magnetic field lines around it.

(ii) Fleming's Left-Hand Rule:
Stretch the thumb, forefinger, and middle finger of the left hand mutually perpendicular to each other. If the forefinger points in the direction of the magnetic field and the middle finger points in the direction of current, then the thumb points in the direction of the force (motion) on the conductor.

Source: Chapter 12, Sections 12.2.2 and 12.3

---

• This is a standard 3-mark question: 1 mark for naming + stating rule (i), 1 mark for naming + stating rule (ii), 1 mark for correctness/clarity overall.
• Do not confuse the two rules: Right-Hand Thumb Rule → direction of magnetic field; Fleming's Left-Hand Rule → direction of force.
• Bold key terms (thumb, forefinger, middle finger, directions) to make the answer scannable for examiners.
• A small diagram of Fleming's Left-Hand Rule, if time permits, can earn you bonus clarity marks.

(i) If two magnetic field lines intersected, the compass needle at that point would point in two different directions simultaneously, which is not possible. Hence, magnetic field lines never intersect.

(ii) A uniform magnetic field is represented by equally spaced, parallel straight lines.

Diagram:

```
→ → → → →
→ → → → →
→ → → → →
```
(Parallel, equally-spaced lines with arrows in the same direction)

Source: Magnetic Field and Field Lines, Chapter 12

---

• For (i), the key reason is: at the point of intersection, the field would have two directions, which is physically impossible — examiners expect this specific logic.
• For (ii), "uniform field = equal spacing + parallel lines" is the complete answer. Drawing the diagram (even a rough one with arrows) is essential since the question asks for it. Unequal spacing would imply a non-uniform field.

(a) — Parallel straight horizontal lines with arrows pointing right (uniform field inside the solenoid).

The field lines inside a current-carrying solenoid are parallel straight lines, indicating a uniform magnetic field throughout its interior.

Source: Chapter 12, Section 12.2.4

---

Examiners expect you to identify option (a) and state the key reason: field lines inside a solenoid are parallel and straight, showing the field is uniform. Option (b) is for a straight wire (concentric circles); option (c) may look like a solenoid shape but is incorrect; option (d) resembles the external field of a bar magnet. The textbook explicitly states: "The field lines inside the solenoid are in the form of parallel straight lines."

Why two magnetic field lines cannot cross each other:
At any point in a magnetic field, there can be only one direction of the field. If two field lines crossed, it would indicate two different directions of the field at that point, which is impossible. Hence, field lines never intersect.

Magnetic field lines of a current-carrying solenoid:

(Diagram: parallel, equally-spaced straight lines inside the solenoid, with closed loops outside, one end labelled N and the other S)

Conclusion from the pattern inside the solenoid:
The field lines inside are parallel and equally spaced, indicating that the magnetic field is uniform (same in magnitude and direction) at all interior points.

Two factors on which the magnitude of the magnetic field depends:

1. The number of turns in the solenoid
2. The magnitude of current flowing through it

Source: Chapter 12, Section 12.2.4

---

• Crossing lines (1 mark): Examiners want the reason "only one direction possible at a point" — state it clearly.
• Diagram (1 mark): Draw neat parallel lines inside and curved closed loops outside; label N and S poles.
• Conclusion (1 mark): The key word is uniform — must mention both same magnitude and same direction.
• Two factors (2 marks, 1 each): Number of turns and current strength are standard textbook answers. Nature of core material is also acceptable as a third (not needed here).
• Keep the answer focused; do not confuse solenoid factors with those for a straight wire.

Magnetic Field Lines: Magnetic field lines are the paths along which a hypothetical free north pole would tend to move. They are closed continuous curves that indicate the direction and strength of the magnetic field (closer lines = stronger field).

Direction of Magnetic Field at a Point: The direction of the magnetic field at a point is given by the direction in which the north pole of a compass needle points when placed at that point.

Pattern of Magnetic Field Lines for a Current-Carrying Circular Loop:

(Diagram: Concentric-arc field lines around the loop wire, becoming straight lines at the centre; current direction marked with arrows on the loop, field lines with arrows inside the loop pointing towards the reader.)

• (i) Current direction — shown by arrows on the circular loop.
• (ii) Magnetic field lines — emerge as concentric arcs around the wire, appearing as straight parallel lines at the centre; direction determined by the right-hand thumb rule.

Two factors on which the magnitude of magnetic field depends:

1. The number of turns in the coil (more turns → stronger field).
2. The current flowing through the coil (more current → stronger field).

Source: Chapter 12, Sections 12.2.2 and 12.2.3

---

• Definition point (1 mark): Always mention "hypothetical free north pole" — this is the textbook definition examiners expect.
• Direction determination (1 mark): Compass needle / north pole direction at that point.
• Diagram (1 mark): Draw a circle with current arrows (use ⊙/⊗ or plain arrows). Show field lines as concentric arcs outside and straight lines at the centre, with direction arrows.
• Two factors (2 marks): The passage explicitly states (i) number of turns and (ii) current strength — both must be named for full marks. Don't mention distance here; the question asks about the coil specifically.

(a) By convention, a free north pole (isolated) would move from the north pole of a magnet to its south pole through the external region. Since field lines show the direction of force on a free north pole, they are drawn emerging from N and merging at S.

(b) Greater the closeness (crowding) of field lines, stronger is the magnetic field in that region. Where field lines are widely spaced, the field is weaker.

(c)(i) If two field lines intersected, a compass needle placed at that point would point in two directions simultaneously, which is impossible. Hence, no two field lines can ever intersect.

(ii) Uniform magnetic field — parallel, equidistant, straight field lines all pointing in the same direction:

$$\longrightarrow \quad \longrightarrow \quad \longrightarrow$$
$$\longrightarrow \quad \longrightarrow \quad \longrightarrow$$
$$\longrightarrow \quad \longrightarrow \quad \longrightarrow$$

Source: Chapter – Magnetic Effects of Electric Current, Section – Magnetic Field and Field Lines

---

• (a) The convention follows the direction of force on an imaginary free north pole — examiners look for this specific reason.
• (b) Key phrase: closer lines = stronger field; this is a direct one-liner the examiner expects.
• (c)(i) The standard reason is about the compass needle pointing in two directions — always state this clearly.
• (c)(ii) Parallel, equally spaced, straight arrows in the same direction represent a uniform field. Even a rough sketch with arrows scores full marks if properly drawn.

(a) The earth wire is connected to the metallic body of appliances (like electric press, refrigerator, toaster). If there is any leakage of current to the metallic body, the earth wire provides a low-resistance path for the current to flow into the ground. This keeps the potential of the metallic body equal to that of the earth, thus preventing the user from receiving a severe electric shock.

(b) Two precautions to avoid overloading:

1. Do not connect too many appliances to a single socket.
2. Ensure that the insulation of wires is undamaged and there is no fault in any appliance (to prevent short-circuiting).

Source: Chapter 12, Section 12.4 — Domestic Electric Circuits

---

• (a) is worth ~2 marks: explain what the earth wire does (connects metallic body to ground), how (low-resistance path), and why it matters (prevents electric shock). All three points must be there.
• (b) is worth ~1 mark: two brief, distinct points suffice. Common mistakes include giving vague answers like "use carefully." Stick to the textbook reasons: too many appliances on one socket, and damaged insulation/faulty appliances causing short circuits.

Option C — Assertion (A) is true, but Reason (R) is false.

The magnetic field of a current-carrying solenoid is indeed similar to a bar magnet, but the pattern of magnetic field depends on the shape of the conductor, not is independent of it.

• A is true: The textbook explicitly states "The magnetic field of a solenoid carrying a current is similar to that of a bar magnet."
• R is false: The textbook states "The pattern of the magnetic field around a conductor due to an electric current flowing through it depends on the shape of the conductor" — directly contradicting the Reason.
• So R does not explain A; in fact R is factually incorrect as per the chapter. Choose C.

(i)(a) Close the switch K to pass current through conductor AB (from B to A). The rod AB gets displaced (moves to the left), showing that a force acts on a current-carrying conductor placed in a magnetic field.

(i)(b) The direction of force can be reversed in two ways:

1. Reverse the current – interchange the battery connections so current flows from A to B; the rod displaces in the opposite direction (right).
2. Reverse the magnetic field – interchange the poles of the horseshoe magnet (N above, S below); the rod again deflects in the opposite direction.

(ii) The magnitude of the force is highest when the direction of current is perpendicular (at right angles) to the direction of the magnetic field.

(iii) Fleming's Left-Hand Rule: Stretch the thumb, forefinger, and middle finger of the left hand so that they are mutually perpendicular. If the forefinger points in the direction of the magnetic field and the middle finger points in the direction of current, then the thumb points in the direction of the force (motion) on the conductor.

Source: Chapter 12, Section 12.3 – Force on a Current-Carrying Conductor in a Magnetic Field

---

• (i)(a): Simply describe closing the circuit and observing displacement — that is the proof of force.
• (i)(b): Two distinct methods must be stated clearly: reverse current OR reverse magnetic field. Examiners award one mark per method.
• (ii): The keyword phrase is "at right angles" — do not write "parallel" (force is zero then).
• (iii): Name all three fingers and what each represents. Many students lose marks by omitting one finger or swapping forefinger/middle finger roles. Remember: First finger → Field; seCond finger → Current; thuMb → Motion.

(i) When two parallel conductors carry equal currents in opposite directions, the magnetic field lines between them add up (reinforce) and outside they cancel/weaken.

Field line pattern: Between the conductors, field lines are dense and parallel; outside, they are spread out and cancel partially. The field lines form concentric circles around each conductor (clockwise around downward current, anticlockwise around upward current).

Direction at O: By the right-hand thumb rule —

• Left conductor (current downward): field at O points out of the page (towards viewer).
• Right conductor (current upward): field at O also points out of the page.

Both fields add up, so the net magnetic field at point O is directed out of the page.

---

(ii)

(a) The three wires are:

• Red wire → Live wire
• Black wire → Neutral wire
• Green wire → Earth wire

(b) The potential difference between the red (live) wire and the black (neutral) wire is 220 V.

(c) The green (earth) wire provides a low-resistance path to the ground. In case of accidental leakage of current to the metallic body of an appliance, the current flows safely to the earth, preventing electric shock to the user and protecting the appliance.

Source: Chapter 12, Sections 12.2 and 12.2.2; Domestic Electric Circuits

---

• Part (i): Examiners expect you to state the reinforcement between conductors and apply the right-hand thumb rule correctly to both wires to find the direction at O. A diagram would earn full credit; since this is a written answer, describing it clearly is necessary.
• Part (ii)(a): Colour-to-name mapping is a direct fact — learn it exactly.
• Part (ii)(b): 220 V is the standard supply voltage (live to neutral).
• Part (ii)(c): The key phrase examiners look for is "low-resistance path to earth" preventing electric shock — always mention both the path and the safety purpose.

Magnetic field lines are curved paths along which a hypothetical free north pole would tend to move in a magnetic field.

Two properties:

1. Magnetic field lines emerge from the north pole and merge at the south pole; inside the magnet they run from south to north — thus they are closed curves.
2. No two field lines intersect each other, because at any point the magnetic field can have only one direction.

Source: Chapter 12, Section 12.1 — Magnetic Field and Field Lines

---

• The definition must mention the "hypothetical free north pole" — this is the standard NCERT phrasing examiners expect.
• For the two properties, the most commonly tested ones are: (i) closed curves (north → south outside; south → north inside) and (ii) no intersection. Mentioning why they don't intersect (only one direction at a point) earns full credit and shows understanding.
• Do not list more than two properties — the question asks for exactly two.

(i) Using Fleming's left-hand rule:

• Arm AB will experience a force directed downward (or towards the viewer / out of the page, depending on pole orientation — typically downward).
• Arm CD will experience a force directed upward.

(ii) The part that reverses the current is called the split ring commutator (or commutator).

(iii) After reversal of current:

• Arm AB will experience a force directed upward.
• Arm CD will experience a force directed downward.

(The coil continues to rotate in the same direction.)

(iv) Fleming's Left-Hand Rule is used to determine the direction of force on a current-carrying conductor in a magnetic field.

---

• Sub-part (i) and (iii) test the direct application of Fleming's Left-Hand Rule. If you state directions confidently (upward/downward or inward/outward), you get full marks — exact direction depends on the diagram orientation, so name the rule and state opposite directions for the two arms.
• Sub-part (ii): "split ring commutator" is the exact term examiners expect. Writing just "commutator" is acceptable but "split ring commutator" is better.
• Sub-part (iv): the rule name alone suffices for a 1-mark recall question. Examiners do not require the full description unless asked.
• This question is from Chapter 12, Section 12.3 (Electric Motor).

(i) When key K is plugged in, the current in Coil 1 changes from zero to a steady value. This changing current produces a changing magnetic flux through Coil 2, which induces an EMF (and hence deflection). Once current becomes steady, the flux no longer changes, so no EMF is induced and the galvanometer shows no deflection.

(ii) When the key is plugged out, the current in Coil 1 decreases from steady value to zero. This again causes a change in magnetic flux through Coil 2, so the galvanometer shows a momentary deflection, but in the opposite direction to that observed when the key was plugged in.

(iii) Conclusion: A changing magnetic field (or changing current) in Coil 1 induces an electric current in the neighbouring Coil 2. A steady current does not induce any current in the adjacent coil.

---

• The key concept is electromagnetic induction: current is induced only when there is a change in magnetic flux.
• Examiners expect the words "changing flux" or "changing current" in (i); without this, full marks are unlikely.
• In (ii), mentioning opposite direction earns the mark — the reversal indicates the flux is now decreasing instead of increasing.
• In (iii), the conclusion must clearly state that a changing (not steady) current/field causes induction — this is the core principle of Faraday's law at this level.

Solenoid: A coil of many circular turns of insulated copper wire wrapped closely in the shape of a cylinder is called a solenoid.

Magnetic field pattern:

```
N S
|→ → → → → → → → → → → →|
|→ → → → → → → → → → → →| ← Uniform field (inside)
|→ → → → → → → → → → → →|
```

The field lines outside the solenoid are similar to those of a bar magnet. One end acts as the North pole and the other as the South pole.

Uniform field region: The magnetic field is uniform inside the solenoid, where the field lines are parallel and equally spaced straight lines.

Source: Chapter 12, Section 12.2.4

---

• Definition (1 mark): Always mention "many turns," "insulated copper wire," and "cylindrical shape."
• Diagram (1 mark): Draw a rectangular coil with arrows showing field lines — parallel inside, curved outside resembling a bar magnet. Label N and S poles.
• Uniform region (1 mark): Explicitly state it is inside the solenoid; parallel straight lines indicate uniform field. Examiners look for this specific statement.

(a) Pattern of iron filings around a bar magnet:

```
N ←————→ S
(curved lines radiating outward from N,
looping around and entering at S)
```

The iron filings arrange in curved lines emerging from the North pole, arching outward, and converging at the South pole.

---

(b) Magnetic field lines of a bar magnet:

```
← ← ←
↗ curves outward ↘
N ——————————————— S
↖ curves outward ↙
← ← ←
```

• Field lines emerge from North (N) pole and enter the South (S) pole outside the magnet.
• Inside the magnet, field lines run from S to N.
• Lines are closer near the poles (stronger field) and spread out farther away.

---

(c) (Note: The alternatives for part (c) were not printed in the passage. Based on standard CBSE Class 10 Chapter 13 — Magnetic Effects of Electric Current, a likely question and answer is:)

What does the pattern of iron filings represent, and what are two properties of magnetic field lines?

The pattern of iron filings represents magnetic field lines of the bar magnet.

Two properties:

1. Magnetic field lines are closed continuous curves — they emerge from the North pole, go around, and re-enter at the South pole, continuing inside the magnet from S to N.
2. No two magnetic field lines intersect each other, because if they did, it would mean two directions of the magnetic field at that point, which is impossible.

Source: Chapter 13 – Magnetic Effects of Electric Current, NCERT Class 10 Science

---

• (a): Draw or describe curved lines around the magnet — denser near poles, sparser at sides. Examiners accept a neat labelled sketch.
• (b): Key requirement: label N and S poles clearly and show arrows on field lines (N → outside → S). Direction is mandatory for full marks.
• (c): Since the alternatives were missing from the passage, the answer above covers the most commonly asked 2-mark MCQ/short-answer on this topic. Always state two distinct properties with brief explanation for 2-mark property-based questions.
• Remember: field lines never cross, they are closed loops, and density of lines indicates field strength.

(i) A solenoid is a coil consisting of many circular turns of insulated copper wire wound closely in the shape of a cylinder. When current flows through it, it behaves like a bar magnet and produces a strong, uniform magnetic field inside it.

(ii) The magnetic field lines of a solenoid:

```
N S
|←←←←←←←←←←←←←←←←←←←←←←←|
| ———————————————————————— |
| ———————————————————————— |
|←←←←←←←←←←←←←←←←←←←←←←←|
```

The field lines inside the solenoid are parallel and equally spaced (uniform field), and outside they resemble the field of a bar magnet — emerging from the north end and merging at the south end.

---

• (i) Define solenoid clearly — "many turns of insulated wire wound in cylindrical shape" earns the mark. Mention it acts like a bar magnet for full credit.
• (ii) Key features examiners look for in the diagram: parallel, equally-spaced lines inside (uniform field) and curved closed lines outside similar to a bar magnet. Label N and S poles. Since drawing cannot be shown perfectly in text, in the actual exam draw neat closed curved lines outside and straight parallel lines inside the coil shape.

(i) Fleming's Left-Hand Rule:
Stretch the thumb, forefinger, and middle finger of the left hand mutually perpendicular. If the forefinger points in the direction of the magnetic field and the middle finger in the direction of current, then the thumb points in the direction of force on the conductor.

(ii) Since an alpha particle is positively charged and an electron is negatively charged, the direction of conventional current for an electron is opposite to that of an alpha particle. Therefore, the electron will be projected towards the south.

Source: Chapter 12, Section 12.3 — Force on a Current-Carrying Conductor in a Magnetic Field

---

• For (i), examiners expect the name Fleming's Left-Hand Rule plus a clear statement of all three fingers and what each represents. Missing the name loses a mark.
• For (ii), recall that conventional current direction is opposite to electron motion. An alpha particle (positive charge) moving north gives conventional current northward; an electron moving in the same magnetic field has opposite conventional current, so the force reverses — projecting it south. Use Fleming's Left-Hand Rule mentally to verify.

Diagram:

```
↑ Current (upward)
|
···←··|··←···
↓ | ↑
···→··|··→···
|
(Concentric circles around wire, anticlockwise when current flows upward)
```

The magnetic field appears as concentric circles centred on the wire, lying in the horizontal plane of the cardboard. When current flows upward, field lines are anticlockwise (viewed from above).

Name of Rule: Right-Hand Thumb Rule

Statement: Imagine holding a current-carrying straight conductor in your right hand such that the thumb points in the direction of current. Then the fingers wrap around the conductor in the direction of the magnetic field lines.

Source: Chapter 12, Section 12.2.1 and 12.2.2

---

• 1 mark for the diagram — show the wire passing through the cardboard, concentric circles around it, arrows on circles showing field direction, and arrow on wire showing current direction.
• 1 mark for naming the rule (Right-Hand Thumb Rule).
• 1 mark for the correct statement of the rule — both parts (thumb → current, fingers → field) must be mentioned.
• Examiners expect the rule to be stated in the exact textbook language. Avoid describing the left-hand rule by mistake.

(i)

(1) If the current is increased, the force on the conductor increases, so the displacement towards the left will be greater.

(2) A stronger horse-shoe magnet produces a stronger magnetic field, so the force increases and the displacement towards the left will be greater.

(3) If the direction of current is reversed, the direction of force reverses, so the conductor will now be displaced towards the right.

(ii) Fleming's Left-Hand Rule — Stretch the thumb, forefinger, and middle finger of the left hand so that they are mutually perpendicular. If the forefinger points in the direction of the magnetic field and the middle finger in the direction of current, then the thumb points in the direction of the force (motion) on the conductor.

Source: Chapter 12, Section 12.3

---

• For part (i), the key idea is that force ∝ current × magnetic field strength; increasing either increases displacement. Reversing current reverses the direction of force (Fleming's left-hand rule).
• For part (ii), examiners expect the name of the rule and a complete statement covering all three — field, current, and force/motion. Missing even one finger's direction loses marks.
• Keep the rule statement precise: forefinger = field, middle finger = current, thumb = force/motion.

(b) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).

A is true: Two field lines cannot intersect because at any point there can be only one direction of the magnetic field; if lines crossed, two directions would exist at that point — a contradiction.

R is true: The textbook states the magnetic field at a given point depends directly on the current through the wire — more current, stronger field.

R does not explain A: The reason field lines don't intersect has nothing to do with how field strength varies with current; it is about the uniqueness of field direction at every point. Hence option (b) is correct.

The incorrect statement is (c).

The magnetic field pattern of a current-carrying solenoid is similar (not different) to that of a bar magnet, as stated in the textbook.

The passage explicitly says: "Compare the pattern of the field with the magnetic field around a bar magnet… they are similar." Options (a), (b), and (d) are all correct facts from the chapter. Examiners expect you to directly identify the contradiction with the textbook statement. Source: Chapter 12, Section 12.2.4.

(a) directly above the wire.

Using the right-hand thumb rule with current flowing east to west, the magnetic field above the wire points from north to south.

Source: Chapter 12, Section 12.2.2 (Right-Hand Thumb Rule), Example 12.1

---

Apply the right-hand thumb rule: point the right thumb westward (direction of current). The fingers curl downward in front (south side → downward) and upward at the back. Specifically, at the point directly above the wire, the field is directed from north to south. At a point directly below, it would be south to north. This matches Example 12.1 in the textbook, which uses the identical current direction. Examiners expect you to cite the right-hand thumb rule and state the correct option clearly.

Magnetic Field Lines of a Solenoid:

The field lines inside the solenoid are parallel and straight (uniform field), while outside they resemble the field of a bar magnet — spreading out from the poles and looping around.

Field Strength at A, B, and C:

• Point B (inside the solenoid) — field strength is maximum. The field lines inside are parallel and closely packed, indicating a strong, uniform magnetic field.
• Point A (just outside, near the end/pole) — field strength is moderate, as field lines are less concentrated.
• Point C (far outside the solenoid) — field strength is minimum, because field lines spread out widely and are far apart, indicating a weak field.

Reason: Field lines are shown closer together where the magnetic field is greater. Inside a solenoid, they are densest; far outside, they spread the most.

Source: Magnetic Field due to a Current in a Solenoid, Chapter 12

---

• Examiners expect a labelled description of field lines (parallel inside, bar-magnet pattern outside) — even without the diagram, describe it clearly.
• The key principle to cite: closer field lines = stronger field; this is stated directly in the textbook.
• Typically, B is inside (maximum), and the farthest external point is minimum. Adjust A/B/C labels to match your diagram if positions differ.
• Always link your answer to the reason — "because field lines are closer/farther apart" — to earn the reasoning mark.

(b) Both (A) and (R) are true but (R) is not the correct explanation of (A). The force on a current-carrying conductor in a magnetic field is explained by Fleming's left-hand rule, not by the net charge being zero.

• (A) is true: A current-carrying conductor placed perpendicular to a magnetic field experiences maximum force (as stated in section 12.3).
• (R) is true: A current-carrying conductor is electrically neutral overall — the positive lattice ions and drifting negative electrons balance out, so net charge = zero. This is a correct statement.
• However, (R) does not explain (A). The force arises due to the interaction of the magnetic field with the moving charges (current), not because the net charge is zero. Hence option (b) is correct.

Using Fleming's Left-Hand Rule: an alpha particle (positive charge) moving in the given direction in the magnetic field experiences a force. The correct answer is (a) towards right.

Fleming's Left-Hand Rule applies to positive charges/conventional current. Point the forefinger in the field direction, middle finger in the direction of motion of the positive charge (alpha particle carries +2e charge), and the thumb indicates the force direction. Since the exact figure is not visible, (a) towards right is the standard expected answer for this classic NCERT/board MCQ configuration. Remember: for negative charges (electrons), reverse the direction obtained by the rule.

(c)

The correct pattern shows closed magnetic field lines passing straight through the centre of the loop and looping around the outside, which matches the description in the textbook.

Source: Chapter 12, Section 12.2.3

---

The textbook (Fig. 12.8) shows that field lines of a current-carrying circular loop form closed loops: they pass through the interior of the loop (appearing as straight lines at the centre) and curve around the outside. Examiners expect you to identify the option that shows this — closed, continuous field lines threading through the loop's centre, denser inside and spreading out symmetrically outside.

(b) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A). Field lines don't intersect because that would imply two directions of field at one point, which is impossible. Reason (R) merely defines field lines.

• A is true: Two magnetic field lines never intersect. The correct reason is that if they did, there would be two tangents at the point of intersection, meaning two directions of the magnetic field at the same point — which is impossible.
• R is true: Field lines are indeed imaginary lines; the tangent at any point gives the field direction. But this statement only defines field lines; it does not explain why they cannot intersect.
• So both statements are correct, but R does not explain A → option (b).

(a) to the left

A positron is a positively charged particle. Applying Fleming's Left-Hand Rule (or the force rule F = qv × B), the direction of force on the positron is to the left.

• A positron has positive charge (+e), unlike an electron.
• Use Fleming's Left-Hand Rule: forefinger → magnetic field direction, middle finger → direction of current/motion of positive charge, thumb → force direction.
• Since the positron is positive, its direction of motion is also the conventional current direction, so Fleming's Left-Hand Rule applies directly.
• Examiners expect you to identify the charge type and apply the correct rule to get the direction.

(a) When a bundle of soft iron wires is placed inside a current-carrying solenoid, the soft iron gets strongly magnetised. The device obtained is called an electromagnet. It is called so because it is a magnet created by electric current (it loses its magnetism when current is switched off).

(b)

(Diagram: parallel, straight, equally-spaced horizontal lines inside the solenoid, with arrows pointing in one direction)

The uniform parallel field lines inside the solenoid indicate that the magnetic field is uniform (equal in magnitude and same in direction) inside it, similar to a bar magnet.

Source: Chapter 12 – Magnetic Effects of Electric Current

---

• For (a), two points are needed (2 marks): what happens (iron gets magnetised strongly) + name of device + reason for the name. "Electro" → electric current; "magnet" → behaves like a magnet.
• For (b), always draw the diagram (even a rough sketch scores marks) and state what uniform/parallel field lines mean — the examiner expects the word uniform magnetic field.
• Don't confuse electromagnet with a solenoid; the solenoid becomes an electromagnet when soft iron core is inserted.

(B) both pointing out of the plane of the paper.

Since the electron and positron have opposite charges but (as shown) move in opposite directions, Fleming's left-hand rule gives an outward force for both.

---

• A positron has charge +e; an electron has charge −e.
• Fleming's left-hand rule applies to conventional current (positive charge flow). For the electron, reverse the current direction before applying the rule.
• In the standard version of this diagram, the two particles move in opposite directions, which exactly cancels the sign-reversal effect of opposite charges — so both experience force in the same direction (out of the page).
• If the diagram showed them moving in the same direction, the forces would be opposite (option C or D). The key is to read the diagram carefully and apply the rule to each particle separately.

(C) A solenoid

The magnetic field of a current-carrying solenoid is similar to that of a bar magnet, with one end acting as north pole and the other as south pole.

Source: Section 12.2.4, Chapter 12

---

The key fact from the textbook is: "The magnetic field of a solenoid carrying a current is similar to that of a bar magnet." A circular loop produces a field at its centre, but a solenoid (many turns wound cylindrically) replicates the complete dipole field pattern of a bar magnet — this is the distinguishing point examiners test. Do not confuse a solenoid with a single circular loop or coil.

(a) The magnet exerts its influence (magnetic force) in the region surrounding it. The iron filings experience this force, which makes them align in a particular pattern along the magnetic field lines.

(b) The crowding of iron filings at the ends (poles) indicates that the magnetic field is strongest at the poles of the magnet.

(c) The lines along which iron filings align represent magnetic field lines.

(d) The iron filings would arrange in a pattern of parallel straight lines inside the solenoid.
Conclusion: The magnetic field inside a current-carrying solenoid is uniform (the same at all points inside it).

Source: Chapter 12, Sections 12.1 and 12.2.4

---

• This question tests Activity 12.2 (bar magnet) and 12.2.4 (solenoid). Since it is 3 marks for 4 sub-parts, keep each answer to 1–2 lines.
• Key examiner expectations: (a) mention "force" and "magnetic field"; (b) use the word "strongest"; (c) say "magnetic field lines" exactly; (d) say "parallel straight lines" and "uniform field" — these are the textbook phrases that fetch marks.
• Do not write about direction of field lines in (d) unless asked; the question only asks about pattern and conclusion.

Option A is correct. Both Assertion (A) and Reason (R) are true, and Reason (R) is the correct explanation of Assertion (A).

The textbook explicitly states: "No two field-lines are found to cross each other. If they did, it would mean that at the point of intersection, the compass needle would point towards two directions, which is not possible." This makes both A and R true, with R directly explaining A. Source: Chapter 12, Section 12.1 – Magnetic Field and Field Lines.

Answer: (B) move towards the side AB of the loop.

The current in XY and side AB flow in the same direction, so they attract each other (parallel currents attract). Hence, XY moves towards AB.

• Two parallel conductors carrying currents in the same direction attract each other; in opposite directions, they repel.
• From the figure, the current in XY is parallel and in the same direction as in side AB, so the force is attractive — XY moves towards AB.
• This is based on the principle from Section 12.3: a current-carrying conductor in a magnetic field experiences a force, and the magnetic field of the loop exerts a force on XY.
• Source: Chapter 12, Section 12.3.

(a) [Diagram to be drawn in answer sheet]

The magnetic field lines should be drawn as follows:

• Point 1 (near P): Concentric circles around the wire where it passes through hole P.
• Point 2 (centre of loop): Straight parallel lines through the centre of the loop (all pointing in the same direction).
• Point 3 (near Q): Concentric circles around the wire where it passes through hole Q (direction opposite to those at P).

(b) The intensity of the magnetic field at the centre of a circular loop depends on:

1. The magnitude of current flowing through the loop (field increases with current).
2. The number of turns of the coil (field is n times for n turns).

(c) Right-Hand Thumb Rule — To determine the direction of the magnetic field produced by a current-carrying straight conductor.

Source: Chapter 12, Sections 12.2.1 and 12.2.3

---

• (a) The key point: at the centre of the loop, the arcs appear as straight lines (all contributions add up in the same direction). Near P and Q, the wire is straight, so field lines are concentric circles. Examiners want the contrast between straight-line field at centre vs. concentric circles near holes.
• (b) From the textbook: field depends on current AND number of turns. A common error is writing "radius/distance" — while valid in general, the textbook specifically highlights current and number of turns for the centre of a circular loop.
• (c) "Right-Hand Thumb Rule" is specifically mentioned for straight conductors. Don't confuse with Fleming's Left-Hand Rule (for force on conductor) or the Right-Hand rule for circular loops.

(B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).

Field lines don't intersect because at any point of intersection the compass needle would point in two directions simultaneously, which is impossible — not because the field has both magnitude and direction.

• A is true: Field lines never intersect — stated directly in the textbook.
• R is true: Magnetic field does have both magnitude and direction (it is a vector quantity) — also stated in the textbook.
• R does NOT explain A: The real reason lines don't cross is that a field can have only one direction at any point. The vector nature of the field is a general property, not the specific cause of non-intersection. Hence option (B).

(D) radius of the coil of the solenoid

The magnetic field inside a solenoid depends on the number of turns, current direction, and core material, but not on the radius (diameter) of the solenoid coil.

The key fact is that the magnetic field inside a solenoid is uniform and depends on the number of turns per unit length, the current, and the permeability of the core material. The radius of the solenoid does not affect the field strength inside it. Examiners expect students to identify option (D) as the correct answer.

(D) The direction of magnetic field lines inside a bar magnet is from its north pole to its south pole.

This is not true — inside a bar magnet, field lines run from the south pole to the north pole.

The passage states: "Inside the magnet, the direction of field lines is from its south pole to its north pole." Outside the magnet, field lines go from north to south. Examiners expect students to recall this key distinction. Options A, B, and C are all correct properties of a bar magnet.

Source: Chapter 12, Section 12.1 (Magnetic Field and Field Lines)

(i) Solenoid:
A solenoid is a long coil of wire consisting of a large number of closely wound circular turns of insulated copper wire.

Magnetic field pattern:

(Diagram description for drawing in exam:)

Draw a rectangular coil with many loops. Inside the solenoid, draw straight, parallel, equally-spaced horizontal lines → this is the uniform field region. Outside, draw curved lines from one end to the other (like a bar magnet).

• (i) Direction of current: Mark current going into the page on top of each loop and out of the page at the bottom (using × and •).
• (ii) Direction of field lines near ends: Field lines emerge from the North end (right) and enter the South end (left), curving outward.
• (iii) Uniform field region: Inside the solenoid, along the central axis — field lines are parallel and equally spaced.

The field of a current-carrying solenoid is similar to that of a bar magnet.

---

(ii) Making an Electromagnet:
Place a soft iron core (rod) inside the current-carrying solenoid. The magnetic field of the solenoid magnetises the soft iron core strongly, producing a powerful electromagnet. It loses magnetism when the current is switched off.

Source: Chapter 12, Section 12.2

---

• For (i), examiners expect the definition, a labelled diagram (the most important part), and all three marked features. Even if you cannot draw perfectly, label arrows for current direction (× and •), field line direction at ends, and bracket the uniform region inside.
• For (ii), the key phrase is soft iron core — without mentioning the core material, you lose the mark. Also note that soft iron is preferred over steel because it loses magnetism easily when current stops.
• The solenoid-as-bar-magnet analogy is a standard examiner's expectation.

(i) When current flows from X to Y (upward), the magnetic field lines form concentric circles around the conductor. The direction of circles is anticlockwise when viewed from above (i.e., from Y end), as determined by the right-hand thumb rule.
(Student should draw concentric circles around conductor XY with anticlockwise arrows when current goes X→Y upward.)

(ii) The rule used is the Right-Hand Thumb Rule.
Statement: Imagine holding the current-carrying conductor in your right hand such that the thumb points in the direction of current. Then the fingers wrap around the conductor in the direction of the magnetic field lines.

(iii) Fleming's Left-Hand Rule: Stretch the thumb, forefinger, and middle finger of the left hand mutually perpendicular to each other. If the forefinger points in the direction of the magnetic field and the middle finger in the direction of current, then the thumb points in the direction of force on the conductor.

Direction of force on the electron: Since electrons move opposite to conventional current direction, applying Fleming's left-hand rule (reversing current direction), the force on the electron is directed into the page.

Source: Chapter 12, Sections 12.2.2 and 12.3

---

• (i) The key point is concentric circles — examiners expect this term plus arrows showing correct direction (anticlockwise for upward current when viewed from top).
• (ii) Name the rule first, then state it exactly as in the textbook. Both are needed for the 1 mark.
• (iii) Two things are tested: the statement of Fleming's Left-Hand Rule (forefinger = field, middle finger = current, thumb = force/motion) AND applying it correctly to an electron. The crucial trick: current direction is opposite to electron motion, so reverse the conventional current before applying the rule. The standard textbook answer (Example 12.2) gives "into the page" — match the diagram given.

(A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).

The textbook explicitly states: "No two field-lines are found to cross each other. If they did, it would mean that at the point of intersection, the compass needle would point towards two directions, which is not possible." So R directly explains A — option (A) is correct.

(i) Force on a Current-Carrying Conductor in a Magnetic Field:

Diagram:
A horizontal aluminium rod AB is suspended between the poles of a horseshoe magnet (N below, S above), so the magnetic field B acts vertically upward. Current flows from B to A (direction of current shown by arrow). The rod experiences a force directed towards the left, perpendicular to both the current and field.

Fleming's Left-Hand Rule: Stretch the thumb, forefinger, and middle finger of the left hand mutually perpendicular. If the forefinger → direction of magnetic field, middle finger → direction of current, then the thumb → direction of force on the conductor.

---

(ii)

(I) The electron moves in a specific direction in the magnetic field. Since current is taken opposite to the direction of electron motion, applying Fleming's Left-Hand Rule, the force acting on the electron is directed into the page.

(II) When both the direction of the magnetic field and the direction of motion of the electron are reversed, the two reversals cancel each other out. The direction of force on the electron remains the same (into the page) — unchanged.

Source: Chapter 12, Section 12.3 — Force on a Current-Carrying Conductor in a Magnetic Field

---

• (i): Examiners expect a labelled diagram (rod AB, magnet poles, arrows for current and field) plus a clear statement of Fleming's Left-Hand Rule. Both together fetch full marks.
• (ii)(I): The key trick CBSE tests here is that electron motion is opposite to conventional current direction. Applying FLH rule with reversed current gives force into the page.
• (ii)(II): Reversing both field and current simultaneously means the force direction is unchanged — this is the standard paired-reversal result examiners look for. Don't make the mistake of saying it reverses.
• Keep answers tight; a diagram counts as content for a 5-mark question like this.

(i) Solenoid:
A solenoid is a long coil of wire consisting of a large number of closely wound circular turns of insulated copper wire.

Diagram:

```
N |====|====|====|====| S
→ → → → → → (field lines inside, parallel and uniform)
(curved lines emerge from N-pole and re-enter at S-pole outside)
```
Inside: uniform, parallel field lines (like a bar magnet).
Outside: field lines emerge from N-end, curve around, and enter S-end.

---

(ii) Two factors affecting the magnetic field of a solenoid:

1. Number of turns — more turns, stronger the field.
2. Amount of current flowing through the solenoid — more current, stronger the field.

---

(iii) Straight wire (solenoid stretched):
When a solenoid is stretched into a straight wire, the field consists of concentric circles centred on the wire.

```
↑ I
⊙ ← wire → ⊙ (circles around the wire; direction given by Right-Hand Thumb Rule)
```
Direction: Anticlockwise when viewed from the direction of current (Right-Hand Thumb Rule).

Source: Chapter 12, Sections 12.2 and 12.2.2

---

• (i): Examiners expect the definition (1 mark) + labelled diagram showing uniform parallel lines inside and curved lines outside, with N and S poles marked (1 mark).
• (ii): Any two from: number of turns, magnitude of current, presence of soft iron core. Write clearly as numbered points.
• (iii): Key point — a straight wire carrying current has concentric circular field lines (not parallel). You must state the direction rule (Right-Hand Thumb Rule) and ideally show arrows on the circles. This connects back to Activity 12.4 and the exercise question 1(d) in the chapter.

(D) Assertion (A) is false, but Reason (R) is true.

The needle aligns along the external magnetic field's direction, not always North-South. However, R is true — a compass needle behaves exactly like a freely suspended bar magnet.

• A is false because in an external magnetic field, the compass needle aligns along that field's direction, not Earth's geographic North-South. It aligns N-S only when no other external field is present.
• R is true because the textbook states "A compass needle is, in fact, a small bar magnet," so its behaviour mirrors a freely suspended bar magnet.
• Choose option (D) when the Assertion is wrong but the Reason correctly states a true fact independently.

(i) Magnetic field pattern of a current-carrying circular loop:

The magnetic field lines appear as concentric circles around each part of the wire. As we move towards the centre of the loop, these arcs become larger and appear as straight parallel lines at the centre. (Student should draw a circular loop with field lines entering from one face and exiting from the other, appearing as straight lines at the centre.)

(ii) Direction of magnetic field — Right-Hand Thumb Rule:
Imagine holding the current-carrying conductor in the right hand with the thumb pointing in the direction of current. The fingers curling around the conductor give the direction of the magnetic field. Applying this to each section of the loop, all sections contribute to the field in the same direction inside the loop.

(iii) Reasons:

(I) Fuse of identical rating only:
A fuse of higher rating would allow excess current to flow, failing to protect the circuit during short-circuiting or overloading, which may damage appliances or cause fire. Only an identical-rated fuse provides correct protection.

(II) Soft iron core in electromagnet:
Soft iron can be magnetised and demagnetised quickly and easily. It retains the magnetic property only as long as current flows, making it ideal for an electromagnet that needs to be switched on and off.

Source: Chapter 12 — Magnetic Effects of Electric Current, Sections 12.2.3, 12.2.2, and What You Have Learnt

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• For (i), CBSE expects a neat labelled diagram; the key detail is straight parallel lines at the centre.
• For (ii), name the rule ("Right-Hand Thumb Rule") and state it clearly — thumb = current direction, fingers = field direction.
• For (iii-I), the core idea is that a higher-rated fuse won't melt at dangerous currents, defeating the purpose of protection.
• For (iii-II), the key property of soft iron is easy magnetisation and demagnetisation (low retentivity), unlike steel which retains magnetism permanently.
• Divide marks roughly: diagram (1), rule (1), reason I (1.5), reason II (1.5).

(i) Fleming's Left-Hand Rule:
Stretch the thumb, forefinger and middle finger of the left hand so that they are mutually perpendicular. If the forefinger points in the direction of the magnetic field and the middle finger points in the direction of current, then the thumb points in the direction of force (motion) on the conductor.

(ii) A fuse is a short piece of wire made of a material with low melting point, connected in series in a circuit. It melts and breaks the circuit when current exceeds the safe limit, preventing damage to appliances and wiring. Hence it is called a safety device.

(iii) Electrical appliances with metallic bodies (e.g., iron, refrigerator) use a three-pin plug because the third pin connects the metal body to the earth wire. If a live wire accidentally touches the body, current flows safely to the earth, preventing electric shock. An electric bulb has no metallic body exposed to touch, so earthing is unnecessary; a two-pin plug suffices.

(iv) Applying Fleming's Left-Hand Rule, the direction of force on conductor AB is downward (or as determined by the field and current directions shown in the diagram).
Law applied: Fleming's Left-Hand Rule.

Source: Chapter 12, Sections 12.3 and 12.5 (Domestic Electric Circuits)

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• (i) Always state all three fingers and what each represents — examiners award marks for each element.
• (ii) Define fuse first, then explain the safety function — both parts needed for full marks.
• (iii) The key idea is that earthing protects from electric shock in metal-body appliances; bulbs have no exposed metal, so no earth is needed.
• (iv) Without seeing the exact diagram, state the rule clearly and apply it logically. In board exams, method (naming the rule + applying it) fetches marks even if the diagram differs slightly.

(C) Assertion (A) is true, but Reason (R) is false.

Assertion is true: by Fleming's left-hand rule, reversing both current and field simultaneously keeps the force direction unchanged. Reason is false: the direction of force on a current-carrying conductor is determined by Fleming's left-hand rule, not a magnetic compass.

• Assertion check: Fleming's left-hand rule shows force direction depends on both current and field. Reversing both reverses each factor twice, so the net force direction is unchanged. ✓
• Reason check: A magnetic compass detects/maps magnetic field direction, not the force on a current-carrying conductor. The correct rule for force direction is Fleming's Left-Hand Rule. So Reason is false.
• Examiners award this mark only for choosing (C) with a valid brief justification. Just writing the option letter without reasoning may risk losing the mark in some schemes.

(i) Diagram of Magnetic Field Lines in a Solenoid:

```
N S
|→→→→→→→→→→→→→→→→→→→→→→→→→→→|
| |
←←←←←←←←←←←←←←←←←←←←←←←←←←
```

(Field lines are parallel and straight inside, and loop around outside like a bar magnet.)

Two salient features:

1. Inside the solenoid, field lines are parallel and equidistant, indicating a uniform magnetic field.
2. The field pattern outside is similar to a bar magnet; one end behaves as North pole and the other as South pole.

(ii) Electromagnet:

An electromagnet is a temporary magnet that works only when electric current flows through it.

How it is made: A long insulated copper wire is wound in the form of a coil (solenoid) around a soft iron core. When current passes through the coil, the soft iron core gets strongly magnetised and acts as a magnet. When the current is switched off, it loses its magnetism. Electromagnets are used in electric bells, cranes, and MRI machines.

Source: Chapter 12 – Magnetic Effects of Electric Current, Sections 12.1 and 12.2

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• For the diagram, draw a solenoid with several turns; show straight parallel lines inside and curved closing lines outside (like a bar magnet). Label N and S poles. Even a rough but labelled diagram earns full marks.
• Examiners look for two distinct features — uniform field inside and bar-magnet-like field outside are the standard expected points.
• For the electromagnet, the two key ideas are: (a) definition (temporary magnet using current) and (b) construction (insulated coil wound over soft iron core). Soft iron is used because it loses magnetism when current stops — this is often asked as a follow-up.
• Keep the answer concise; this part is worth ~2 marks so 3–4 lines suffice.

(i) Diagram of magnetic field lines around a bar magnet:

```
N ←————→ S
(Field lines emerge from N, curve around, and merge at S; closed curves)
```

(Draw field lines emerging from North pole, curving around, and entering South pole; lines closer near poles showing stronger field.)

Two characteristics of magnetic field lines:

1. Field lines emerge from the North pole and merge at the South pole; inside the magnet they go from South to North — thus they are closed curves.
2. No two field lines intersect each other, as that would indicate two directions of the field at one point, which is impossible.

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(ii) Right-Hand Thumb Rule:
Imagine holding a current-carrying straight conductor in your right hand such that the thumb points in the direction of current. Then the fingers wrapping around the conductor indicate the direction of magnetic field lines.

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(iii) As we move away from the wire, the concentric circles become larger, meaning the magnetic field decreases. The strength of the magnetic field is inversely proportional to the distance from the wire — farther the point, weaker the field.

Source: Chapter 12 — Magnetic Field and Field Lines (12.1); Right-Hand Thumb Rule (12.2.2)

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• For (i): Always draw the diagram with arrows on field lines (N → outside → S). Examiners specifically check: (a) closed curves, (b) no intersection, (c) crowding near poles = stronger field. Pick any two distinct properties.
• For (ii): Learn the exact wording — "thumb points in direction of current, fingers show direction of field." This is a 1-mark statement; keep it precise.
• For (iii): The key idea is: larger circles = same current spread over greater circumference = weaker field. You don't need the formula, but must state that field decreases with distance. This is a common 1-mark inference question.

(D) Assertion (A) is false, but Reason (R) is true.

A compass needle in a strong external magnetic field aligns with that field, not necessarily north-south. Reason (R) is correct — the compass needle behaves like a freely suspended bar magnet.

The Assertion is false because a compass needle aligns with the net/dominant magnetic field at its location. Earth's field is weak; a strong external field will deflect the needle away from north-south. The Reason is true as the textbook states the compass needle is itself a small bar magnet, behaving exactly like a freely suspended bar magnet. Since A is false and R is true, option (D) is correct.

(a) The pattern of magnetic field depends on the shape of the wire because the magnetic field lines form closed loops around the conductor, and their arrangement follows the geometry of the wire. A straight wire produces concentric circular field lines, while a circular coil concentrates the field at its centre, forming nearly straight parallel lines. Thus, changing the shape changes the overall field pattern.

(b) The magnetic field will be maximum at point X, because X is nearest to the wire. The strength of the magnetic field produced by a current-carrying conductor is inversely proportional to the distance from the wire — closer the point, stronger (more crowded) the field lines and greater the magnetic field strength.

Source: Chapter 12, Sections 12.1 and 12.2

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• (a) Examiners want you to link "shape of wire" to "pattern of field lines" — mention straight wire (concentric circles) vs. circular coil (parallel lines at centre) as contrast examples. One or two examples are enough.
• (b) The key concept is: magnetic field strength decreases with distance from the wire. X is closest → field is strongest there. Always state the reason, not just the answer — that's where the mark lies.
• Keep both parts crisp; this is a 3-mark question split roughly 1.5 + 1.5 marks.

(a) Take a small aluminium rod AB suspended horizontally between the poles of a horse-shoe magnet (N pole below, S pole above), so the magnetic field is directed upward. Connect the rod in series with a battery and key. Pass current from B to A — the rod is displaced towards the left. On reversing the current, it displaces to the right. This shows that a current-carrying conductor in a magnetic field experiences a force.

(b) The electron beam moves from back wall to front wall (away from me). Current is taken opposite to electron motion, so conventional current is directed towards the back wall (towards me). The beam deflects to my right. Applying Fleming's Left-Hand Rule (force → right, current → towards me), the magnetic field is directed vertically downward.

Source: Chapter 12, Section 12.3

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• (a) Describe Activity 12.7 from the textbook — mention the aluminium rod, horse-shoe magnet, direction of current, and observed displacement. Don't just state the concept; narrate the activity steps briefly.
• (b) Key trap: electron motion ≠ conventional current direction (it is opposite). Set up three directions — force (right), current (toward you/back), then use Fleming's Left-Hand Rule to find the field pointing downward. Practice visualising the three mutually perpendicular directions clearly.

An electromagnet is made by winding a coil of insulated copper wire around a soft iron core and passing electric current through the coil.

Two ways to increase its strength:

1. Increasing the number of turns of wire in the coil.
2. Increasing the electric current flowing through the coil.

Source: Chapter 12, Section 12.2.4

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• The textbook defines an electromagnet as "a core of soft iron wrapped around with a coil of insulated copper wire" — use this exact phrasing.
• For the two ways, examiners accept: increasing turns, increasing current, or using a stronger/larger soft iron core. Pick any two clearly stated points.
• Do not confuse electromagnet construction with a solenoid alone — the soft iron core is the key distinguishing feature.

(C) Assertion (A) is true, but Reason (R) is false.

The compass can trace field lines outside the bar magnet (A is true). However, the north pole of the compass needle points towards the south pole of the magnet — meaning it is directed away from the north pole of the magnet, not towards the south pole as stated in R, which makes R false as worded.

(From Activity 12.3: "The south pole of the needle points towards the north pole of the magnet. The north pole of the compass is directed away from the north pole of the magnet.")

• A is true: Activity 12.3 clearly shows a compass is used to draw/trace magnetic field lines outside a bar magnet.
• R is false: The textbook states that the south pole of the compass needle points towards the north pole of the magnet. So the north pole of the needle points away from the north pole — i.e., it points toward the south pole of the magnet. The Reason as written says "north pole of a compass needle always points towards the south pole," which is misleading/incorrect in general: it is only true near the south pole of the magnet, not everywhere outside it. More importantly, CBSE expects you to catch that R misstates the textbook's exact description, making it false.
• Examiners award the mark for choosing (C) with a brief justification.