The unit of power of a lens is

Options

A. metre
B. dyne
C. dioptre
D. none of these

Explanation

To solve the question regarding the unit of power of a lens, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Concept of Power of a Lens**:
- The power of a lens is a measure of its ability to converge or diverge light. It is defined as the reciprocal of the focal length of the lens.

2. **Identify the Unit of Power**:
- The unit of power of a lens is called the "diopter," which is represented by the symbol "D".

3. **Relation Between Power and Focal Length**:
- The formula to calculate the power (P) of a lens is given by:
\[ P = \frac{1}{f} \]
where \( P \) is the power in diopters and \( f \) is the focal length in meters.

4. **Convert Focal Length to Meters**:
- If the focal length is given in centimeters, convert it to meters before using it in the formula. For example, if the focal length is 10 cm, it should be converted to meters:
\[ f = 10 \text{ cm} = 0.1 \text{ m} \]

5. **Calculate the Power**:
- Substitute the focal length in meters into the power formula:
\[ P = \frac{1}{0.1} = 10 \text{ D} \]

6. **Conclusion**:
- Therefore, the unit of power of a lens is diopter (D).

### Final Answer:
The unit of power of a lens is **diopter (D)**.

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