Torque on a current loop in a uniform field — NEET & JEE Questions

Question 1 · difficulty L1 · recall

The torque magnitude on a single-turn current loop of area A in uniform field B is

• A. IAB cosθ
• B. IB/A
• C. IAB sinθ
• D. IA/B

Question 2 · difficulty L1 · understanding

For an N-turn coil, the magnetic dipole moment magnitude is

• A. IA/N
• B. NIB
• C. N²IA
• D. NIA

Question 3 · difficulty L2 · understanding

Torque on a current loop is maximum when its magnetic moment is

• A. perpendicular to B
• B. parallel to B
• C. antiparallel to B
• D. zero but area finite

Question 4 · difficulty L2 · application

A loop has magnetic moment 0.30 A m² in a 0.20 T field at 30°. Its torque is

• A. 0.060 N m
• B. 0.030 N m
• C. 0.015 N m
• D. 0.12 N m

Question 5 · difficulty L2 · understanding

The torque magnitude on a current-carrying loop in a uniform magnetic field is

• A. $\tau=NIAB\sin\theta$
• B. $\tau=NIAB\cos\theta$ always
• C. $\tau=I/B$
• D. $\tau=NIA/B$

Question 6 · difficulty L3 · application

If the number of turns and current are both doubled at fixed area and field orientation, torque becomes

• A. twice
• B. half
• C. four times
• D. unchanged

Question 7 · difficulty L3 · application

A rectangular loop in a uniform magnetic field can experience zero net force but nonzero torque because

• A. all segment forces point the same way
• B. magnetic field does work around the loop
• C. current vanishes on two sides
• D. opposite forces form a couple

Question 8 · difficulty L3 · application

A single-turn loop has current 2 A, area 0.10 m² and is oriented so that its magnetic moment is perpendicular to a 0.5 T field. What torque acts?

• A. 0.01 N m
• B. 0.05 N m
• C. 0.10 N m
• D. 1.0 N m

Question 9 · difficulty L3 · application

When the magnetic moment of a current loop is parallel to a uniform magnetic field, the torque on the loop is

• A. maximum
• B. zero
• C. equal to NIAB
• D. independent of orientation

Question 10 · difficulty L4 · analysis

A current loop is initially aligned with its magnetic moment parallel to B. A small rotation away from this position produces a torque that tends to

• A. restore the loop toward parallel alignment
• B. drive it toward 90° indefinitely
• C. reverse the current automatically
• D. increase its area