The focal length of a lens is 50 cm. Its power would be

Options

A. 50 dioptres
B. 2 dioptres
C. 20 dioptres
D. none of these

Explanation

To find the power of a lens given its focal length, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Formula for Power**:
The power \( P \) of a lens is given by the formula:
\[ P = \frac{1}{f} \]
where \( f \) is the focal length in meters, and the power is measured in diopters (D).

2. **Convert Focal Length to Meters**:
The focal length given is 50 cm. We need to convert this to meters:
\[ f = \frac{50 \text{ cm}}{100} = 0.5 \text{ m} \]

3. **Calculate the Power**:
Now, we can substitute the focal length into the power formula:
\[ P = \frac{1}{0.5} = 2 \text{ D} \]

4. **Conclusion**:
The power of the lens is 2 diopters.

### Final Answer:
The power of the lens is **2 diopters**.

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