Assertion (A) : An alternator is machine which converts mechanical energy into electrical energy.
Reason (R) : When a coil rotates in a magnetic field an e.m.f. is induced in it.

Options

A. Both A and R are true and R is the correct explanation of A.
B. Both A and R are true and R is NOT the correct explanation of A.
C. A is true but R is false
D. A is false and R is true

Explanation

To solve the question, we need to analyze the Assertion (A) and Reason (R) provided:

### Step 1: Analyze the Assertion (A)
The assertion states: "An alternator is a machine which converts mechanical energy into electrical energy."

- **Explanation**: An alternator, also known as a generator, indeed converts mechanical energy into electrical energy. This is a fundamental principle of how generators operate. They use mechanical energy (often from a turbine or engine) to rotate a coil within a magnetic field, leading to the generation of electrical energy.

### Step 2: Analyze the Reason (R)
The reason states: "When a coil rotates in a magnetic field, an e.m.f. is induced in it."

- **Explanation**: This statement is also true. According to Faraday's law of electromagnetic induction, when a coil rotates in a magnetic field, the magnetic flux through the coil changes, which induces an electromotive force (e.m.f.) in the coil. This is the mechanism by which electrical energy is generated in an alternator.

### Step 3: Determine the Relationship Between A and R
- Both the assertion and reason are correct statements. Furthermore, the reason provides a correct explanation for the assertion. The assertion describes what an alternator does, while the reason explains how it operates.

### Conclusion
Both the assertion (A) and reason (R) are correct, and R is the correct explanation of A.

### Final Answer
Both A and R are correct, and R is the correct explanation of A.

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