Transformers are used

Options

A. in DC circuits only
B. in AC circuits only
C. in both DC and AC circuits
D. neither in DC nor in AC circuits

Answer

To solve the question about the use of transformers, we need to analyze each option provided and understand how transformers operate.

### Step-by-Step Solution:

1. **Understanding the Function of Transformers**:
- Transformers operate on the principle of electromagnetic induction. They require a changing magnetic field to induce voltage in the secondary coil.

2. **Evaluating Option 1 (DC Circuit Only)**:
- In a DC circuit, the current is constant and does not change over time. Since transformers rely on changing magnetic fields to induce electromotive force (EMF), a constant DC current will not produce a changing magnetic field. Therefore, transformers cannot operate in a DC circuit.
- **Conclusion**: Option 1 is incorrect.

3. **Evaluating Option 2 (AC Circuit Only)**:
- In an AC circuit, the current alternates and changes direction periodically. This change in current creates a changing magnetic field, which induces EMF in the secondary coil of the transformer. Thus, transformers are designed to work specifically with alternating current (AC).
- **Conclusion**: Option 2 is correct.

4. **Evaluating Option 3 (Both DC and AC Circuits)**:
- Since we established that transformers do not operate in a DC circuit, this option is also incorrect. Transformers only function with AC.
- **Conclusion**: Option 3 is incorrect.

5. **Evaluating Option 4 (Neither DC nor AC Circuits)**:
- This option suggests that transformers do not work in either type of circuit. Since we have established that transformers do work in AC circuits, this option is also incorrect.
- **Conclusion**: Option 4 is incorrect.

### Final Answer:
The correct option is **Option 2: in AC circuit only**.

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