A metal plate is getting heated. It can be because of-
A. An alternating current is passing through the plate.
B. It is placed in a time varying magnetic field.
C. A direct current is passing through the plate.
D. It is placed in a space varying magnetic field, but does not vary with time.
E. It is placed in a time constant magnetic field.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → A, B, C Only
A metal plate gets heated when a current flows through it (Joule heating, \( H = I^{2}Rt \)). The current may come from a source connected to the plate, or it may be an eddy current induced in the plate by a changing magnetic flux (Faraday's law).
(A) An alternating current is passing through the plate. — Correct. An alternating current dissipates power \( I_{\mathrm{rms}}^{2}R \) in the plate, so the plate is heated by Joule heating.
(B) It is placed in a time varying magnetic field. — Correct. The flux through the plate changes with time, so eddy currents are induced in the plate and they heat it.
(C) A direct current is passing through the plate. — Correct. A steady current also meets the resistance of the plate, so heat is produced at the rate \( I^{2}R \).
(D) It is placed in a space varying magnetic field, but does not vary with time. — Incorrect. For a plate at rest the flux does not change, so no emf and no eddy current are induced, and the plate is not heated.
(E) It is placed in a time constant magnetic field. — Incorrect. A constant field gives a constant flux, so no current is induced.
Note: A similar question was also asked in CUET (UG) 2023 on 27-05-2023 (Slot 3).