Science — CBSE Class 10 board question

(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.

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(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

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• 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.