Question

The diagram shows a copper conductor placed along the east-west direction. Magnetic compass P is present above the conductor, and Q is below the conductor. If current is passed through the wire from A to B, then which of the two compasses will show prominent deflection and why?

Answer 1

Compass P will show prominent deflection. Using the right-hand thumb rule, for the current direction from A to B, the magnetic field due to the current above the wire is opposite to the Earth's magnetic field, while below the wire it is in the same direction as the Earth's magnetic field. Since the compass needle aligns with the resultant magnetic field, the field above the wire opposes the Earth's field and causes a prominent deflection in P. Below the wire, the fields are in the same direction, so Q does not show prominent deflection.