Force on Magnetic vs Non-Magnetic Sheets Near a Pole
Physics · Magnetism And Matter · NEET
Near a strong magnetic pole, a MAGNETIC sheet (iron, or any para/ferro material) is pulled toward the pole, so you must apply a force to hold it still. A plain NON-MAGNetic, non-conducting sheet (wood, plastic) feels no force at all. But if the sheet is CONDUCTING and you move it, eddy currents appear and push back, so a force is again needed. Memory hook: "Only two things feel the pole: magnetic stuff (attracted at rest) and moving metal (eddy drag)."
Iron is pulled toward the pole (hold-force needed at rest); a plastic sheet feels nothing; a moving copper sheet feels eddy-current drag (orange) opposing its motion.
Your doubts, answered
Does a non-magnetic sheet get pulled by a magnet at all?
No. If the sheet is non-magnetic AND non-conducting (like plastic, wood, glass), it has no magnetic response and no eddy currents. It stays put on its own, so no force is needed to hold it. This is why option B in the NEET 2024 question is wrong.
Why does a magnetic (iron) sheet need a force to hold it near the pole?
The field near a pole is non-uniform (strong close to the pole, weak far away). A magnetic material gets magnetised and is pulled toward the stronger field, i.e. toward the pole. To keep it from moving in, you must apply an equal outward force to hold it. So a force IS needed.
A conducting sheet is non-magnetic. Why does it still need a force?
Only when it MOVES. Moving a conductor through a non-uniform field changes the flux through it, which induces eddy currents. By Lenz's law these currents oppose the motion, creating a drag force. To keep it moving at uniform velocity you must push against this drag. At rest a non-magnetic conductor feels no force.
What is the difference between the attraction on iron and the drag on copper?
Iron (ferro/para) is attracted because it becomes a magnet in the field, this happens even at rest. Copper (a non-magnetic conductor) feels nothing at rest, its force appears only during motion as eddy-current drag. Different cause, both need an applied force in their respective situations.
For a non-conducting, non-polar sheet moving away from the pole, is a force needed?
No. Non-conducting means no eddy currents, and non-polar/non-magnetic means no magnetic pull. It slides away with no force needed. This is why option D in the NEET 2024 question is false.
⚠️ The NEET trap ✗ Assuming any sheet placed near a strong pole needs a force to hold it, so a non-magnetic sheet must also feel a pull. ✓ A non-magnetic, non-conducting sheet feels ZERO force at rest. Force appears only for magnetic sheets (attraction) or for moving conductors (eddy-current drag). 🧠 Ask two questions: Is it magnetic? Is it a MOVING conductor? If both are 'no', the force is zero.
Real NEET questions
NEET 2024
A sheet is placed on a horizontal surface in front of a strong magnetic pole. Choose the correct statement(s) about when a force is needed: A. to hold it there if it is magnetic; B. to hold it there if it is non-magnetic; C. to move it away with uniform velocity if it is conducting; D. to move it away with uniform velocity if it is both non-conducting and non-polar.
A · A and C only ✓
B · A, C and D only
C · C only
D · B and D only
Solution: Step 1: A magnetic sheet (para/ferro) is magnetised and attracted toward the stronger field at the pole, so a force is needed to hold it. A is TRUE.
Step 2: A non-magnetic sheet has no magnetic response, so no force is needed to hold it. B is FALSE.
Step 3: Moving a CONDUCTING sheet through the non-uniform field changes flux, inducing eddy currents that oppose the motion (Lenz's law). A force is needed to keep uniform velocity. C is TRUE.
Step 4: A non-conducting, non-polar sheet gives no eddy currents and no magnetic pull, so no force is needed. D is FALSE.
Correct statements: A and C only. Answer: (A).
NEET 2018
A thin diamagnetic rod is placed vertically between the poles of an electromagnet. When the current is switched on, the rod is pushed up out of the field, gaining gravitational PE. The work required comes from:
A · the lattice structure of the rod
B · the magnetic field
C · the current source ✓
D · the induced electric field due to the changing field
Solution: Step 1: A diamagnetic material is repelled from the stronger field toward the weaker field, so it is pushed out of the gap.
Step 2: The magnetic force on charges does no net work by itself.
Step 3: As the diamagnet moves and reacts back on the field, the energy to raise it (and its gravitational PE) is supplied by the CURRENT SOURCE that maintains the field. Answer: (C).
Solved Magnetism And Matter NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Yes. Iron is ferromagnetic, so it becomes magnetised in the field and is pulled toward the stronger field near the pole, even when both are at rest. A force is needed to hold it back.
Is aluminium or copper attracted to a magnet?
Not at rest, because they are non-magnetic (aluminium is very weakly paramagnetic, copper diamagnetic). But when a copper or aluminium sheet MOVES through a non-uniform field, eddy currents produce a drag force opposing the motion.
What is the role of non-uniform field here?
A uniform field gives a magnetic dipole only a torque, not a net force. The pull on a magnetic sheet and the eddy-current drag both depend on the field being non-uniform (strong near the pole, weak away). Near a pole the field is always non-uniform.
Why do eddy currents cause a force only during motion?
Eddy currents need a changing flux. A stationary conductor in a steady field has constant flux, so no eddy currents and no force. Motion changes the flux, induces currents, and Lenz's law makes them oppose the motion.
Which sheet needs no force in any case?
A non-magnetic, non-conducting sheet (plastic, wood, glass). It has no magnetic pull and no eddy currents, so it feels zero force whether at rest or moving.
