A metal plate is getting heated . It can be because

Options

A. passing either a direct or alternating current through the plate.
B. placing in time varying magnetic field.
C. placing in a space varying magntic field, but does not vary with time.
D. both (a) and (b) are correct.

Explanation

To solve the question of why a metal plate is getting heated, we can break down the reasoning into clear steps:

### Step 1: Identify the Possible Causes of Heating
The question suggests several scenarios that could lead to the heating of a metal plate. These include:
- Passing direct or alternating current through the plate.
- Placing the plate in a time-varying magnetic field.
- Placing the plate in a space-varying magnetic field that does not vary with time.

### Step 2: Analyze the Effect of Current
When a direct or alternating current is passed through the metal plate:
- The plate contains free electrons that can move.
- As the current flows, these electrons collide with each other and with the lattice structure of the metal.
- These collisions convert electrical energy into thermal energy, causing the plate to heat up.

### Step 3: Analyze the Effect of a Time-Varying Magnetic Field
When the metal plate is placed in a time-varying magnetic field:
- The changing magnetic field induces an electromotive force (emf) in the plate according to Faraday's law of electromagnetic induction.
- This induced emf causes a current to flow in the plate.
- Similar to the previous case, this current will also lead to collisions among electrons, generating heat.

### Step 4: Conclusion
Both scenarios (passing current and placing in a time-varying magnetic field) can cause the metal plate to heat up. Therefore, the correct answer is that both statements are true.

### Final Answer
Both A (passing current) and B (placing in a time-varying magnetic field) are correct reasons for the heating of the metal plate.

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