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Exam level2 past questions

Magnetic dipoles and torque

Study the behavior of magnetic dipoles in magnetic fields, including torque, potential energy, and the vector addition of dipole moments.

Why this shows up in the exam

NEET questions often involve analyzing the orientation, energy, and resultant effects on magnetic dipoles in various field configurations.

How NEET tests this

Numerical · 2 QsAssertion–reasonApplication

Learn the idea

A magnetic dipole experiences a torque τ = M × B that tries to align it with the field, and it feels a net force only when the magnetic field varies with position.

🧠 Memory hook: Uniform field → ‘U‑only torque’, Non‑uniform field → ‘N‑force and torque’ (U vs N).

Get this one clearly and it pays off every single time it shows up in the paper. 🎯

Formulas & facts to keep ready

  • Torque on a dipole: τ = M × B
  • Potential energy: U = ‑M·B
  • In a uniform magnetic field the net force on a dipole is zero
  • In a non‑uniform magnetic field a dipole experiences a net force
  • Magnetic dipole moment of a current loop: M = I·A (area vector)

How to approach it

  1. 11. Check whether the external magnetic field is uniform or non‑uniform.
  2. 22. If uniform, write τ = M × B and set net force = 0.
  3. 33. If non‑uniform, state that both τ = M × B and a net force act (direction follows the field gradient).
  4. 44. Use the sign of U = ‑M·B to decide the stable orientation.

Worked example — watch it click

Assertion (A): When a magnetic dipole is placed in a non-uniform magnetic field, only a torque acts on the dipole. Reason (R): Force would also act on dipole if magnetic field were uniform.

  • A)Both (A) and (R) are true, and (R) is the correct explanation of (A).
  • B)Both (A) and (R) are true, but (R) is not the correct explanation of (A).
  • C)(A) is true but (R) is false.
  • ✅Both (A) and (R) are false.

The concept behind this problem

The example asks you to judge the truth of two statements about force and torque; it checks whether you know that uniform fields give only torque and non‑uniform fields give both force and torque.

Step by step

  1. 1Assertion (A): In a non-uniform magnetic field, both force AND torque act on a magnetic dipole.
  2. 2The force arises due to the gradient of the field.
  3. 3So (A) is FALSE.
  4. 4Reason (R): In a uniform magnetic field, only torque acts on the dipole (τ = M × B), but no net force acts because the field is uniform.
  5. 5So (R) is also FALSE.
  6. 6Both statements are false.

Watch out

Students often think a dipole always feels only torque, forgetting that a non‑uniform field also exerts a net force.

Common slip-ups that cost marks

  • •Don’t assume torque is absent in a uniform field – it is always present unless M is parallel to B.
  • •Don’t claim a force exists in a uniform field – the spatial gradient must be non‑zero.
  • •Avoid writing the explicit gradient formula for force; just remember that a varying field produces a force.

🌟 That's the whole idea — you've got this. Try the practice set below; every question you attempt makes it stick a little harder.

Practise it

These are real questions from past NEET papers that test this exact idea.

Question 1 of 2NEET 2023

Assertion (A): When a magnetic dipole is placed in a non-uniform magnetic field, only a torque acts on the dipole. Reason (R): Force would also act on dipole if magnetic field were uniform.

Push further

More challenging

6 harder questions built from the past papers above — a step up in difficulty, with distractors designed so you can't get there by elimination. Written and checked by our reviewers, not from a real paper.

Question 1 of 6

Consider a current loop placed in a magnetic field that varies in strength along its length but is uniform in direction. What will be the effect on the current loop?

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