Choose the correct statements:
(A) When a metallic plate is placed in a changing magnetic field, an induced current is produced.
(B) Alternating induced current is produced when a metallic plate oscillates between two unlike poles of a magnet.
(C) The core of the transformer is laminated to reduce flux loss.
(D) Lenz’s law obeys conservation of energy.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (A), (B), and (D) only
A changing magnetic flux through a solid metal induces circulating eddy currents in it, and by Lenz’s law these currents always oppose the change that produces them.
(A) When a metallic plate is placed in a changing magnetic field, an induced current is produced. — Correct. The changing flux through the plate induces eddy currents.
(B) Alternating induced current is produced when a metallic plate oscillates between two unlike poles of a magnet. — Correct. As the plate swings into and out of the field, the flux through it rises and falls alternately, so the eddy currents reverse direction each half swing (and damp the motion).
(C) The core of the transformer is laminated to reduce flux loss. — Incorrect. Thin insulated laminations increase the resistance of the eddy-current paths and so reduce eddy-current (heating) loss. Flux leakage is reduced by winding the primary and secondary one over the other, not by laminating.
(D) Lenz’s law obeys conservation of energy. — Correct. Because the induced current opposes the change, work must be done to produce it; that work is the source of the electrical energy.
Note: This question is from the pre-rationalised NCERT book (2022-23). The topic was removed from the latest NCERT book (2026-27), and it also appears to be out of the CUET 2026 syllabus.
NCERT (Pre-rationalised edition, 2022-23):
Eddy Currents – “… Even when bulk pieces of conductors are subjected to changing magnetic flux, induced currents are produced in them.”
Eddy Currents – “… Magnetic flux associated with the plate keeps on changing as the plate moves in and out of the region between magnetic poles. The flux change induces eddy currents in the plate. Directions of eddy currents are opposite when the plate swings into the region between the poles and when it swings out of the region.”
Transformers – “… (iii) Eddy currents: The alternating magnetic flux induces eddy currents in the iron core and causes heating. The effect is reduced by having a laminated core.”
Energy Consideration: A Quantitative Study – “In Section 6.5, we discussed qualitatively that Lenz’s law is consistent with the law of conservation of energy.”