A metal plate is getting heated: it can be because
A. a direct current is passing through the plate
B. it is placed in a time varying magnetic field
C. it is placed in space varying magnetic field, but doesn't vary with time.
D. an alternating current is passing through the plate
E. it is placed between the pole pieces of a magnet
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → A, B and D Only
A metal plate gets heated when a current flows in it. The current can be passed through it from a source (Joule heating, \( I^{2}R \)), or induced in it by a changing magnetic flux (eddy currents).
(A) a direct current is passing through the plate — Correct. A steady current through the resistance of the plate produces Joule heat \( I^{2}R \).
(B) it is placed in a time varying magnetic field — Correct. The changing flux through the plate induces eddy currents, which heat it.
(C) it is placed in space varying magnetic field, but doesn't vary with time. — Incorrect. For a plate at rest, a field that does not change with time gives no change of flux, so no current is induced.
(D) an alternating current is passing through the plate — Correct. An alternating current also produces Joule heat, since the heating depends on \( I^{2} \).
(E) it is placed between the pole pieces of a magnet — Incorrect. The field of a magnet is steady, so a plate at rest in it has no induced current and is not heated.
Note: A similar question was also asked in CUET (UG) 2023 on 23-05-2023 (Slot 3).