Two identical rectangular coils, X and Y, are placed in the same magnetic field between the poles of a permanent magnet. Each coil is connected to a d.c. supply so that a current flows through it. - Coil X has 50 turns and carries a current of 2 A. - Coil Y has 50 turns and carr…

IGCSE Physics 0625: Comparing Turning Effect in a d.c. Motor Coil

Step 1: Recall the factors affecting the turning effect of a current-carrying coil

The turning effect (torque) on a coil in a magnetic field is increased by increasing:

the number of turns on the coil,
the current flowing through the coil, or
the strength of the magnetic field.

Step 2: Compare coils X and Y factor by factor

Both coils have the same number of turns ( $50$ ) and sit in the same magnetic field, so those two factors are identical for X and Y, they cannot explain any difference between the coils.

The current is different: coil X carries $2\text{ A}$ , while coil Y carries $4\text{ A}$ , twice as much current.

Step 3: Apply the rule to the differing factor

Since a larger current gives a larger turning effect (with everything else unchanged), coil Y, which carries the greater current, experiences the greater turning effect.

Why the other options are wrong

Option	Description	Error
A	X has greater turning effect	Gets the comparison backwards. A smaller current gives a smaller turning effect, not a greater one
C	Turning effects are equal	Ignores the difference in current between the two coils
D	Neither has a turning effect	Both coils clearly carry a current in a field, so both experience a turning effect; equal turns does not mean zero turning effect

Final answers

Coil Y, carrying the larger current, experiences the greater turning effect, option B.