State the rule to determine the direction of a (a) magnetic field produced around a straight conductor carrying current and (b) force experienced by a current carrying straight conductor placed in a magnetic field which is perpendicular to it.
Generated by claude-sonnet-4-6 · 2026-06-15 06:51 · grounding rag
Model Answer
(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
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Explanation
- 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.