Assertion : An ac generator is based on the phenomenon of self-induction.
Reason : In single coil, we consider self-induction only.

Options

A. If both assertion and reason are true and the reason is the correct explanation of the assertion.
B. If both assertion and reason are true but reason is not the correct explanation of the assertion.
C. If assertion is true but reason is false.
D. If assertion is false but reason is true.

Explanation

To solve the question, we need to analyze the assertion and the reason given:

**Assertion**: An AC generator is based on the phenomenon of self-induction.
**Reason**: In a single coil, we consider self-induction only.

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- An AC generator operates on the principle of electromagnetic induction, not solely on self-induction.
- Electromagnetic induction occurs when a conductor (like a coil) moves through a magnetic field or when the magnetic field around a conductor changes, inducing an electromotive force (EMF).
- Therefore, the assertion is **false**.

2. **Understanding the Reason**:
- The reason states that in a single coil, we consider self-induction only.
- Self-induction refers to the phenomenon where a changing current in a coil induces an EMF in the same coil due to the change in magnetic flux.
- This statement is **true** because self-induction is indeed a phenomenon observed in a single coil.

3. **Conclusion**:
- Since the assertion is false and the reason is true, the correct relationship between the two is that the assertion does not correctly explain the reason.
- Therefore, the correct answer is option **D**: the assertion is false, but the reason is true.

### Final Answer:
**D**: The assertion is false, but the reason is true.

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