Power of a lens is + 5 D, its focal length is :

Options

A. 20 m
B. 2 m
C. 0.2 m
D. none of these

Answer

To find the focal length of a lens given its power, we can use the relationship between power (P) and focal length (f). The formula is:

\[ P = \frac{1}{f} \]

Where:
- P is the power of the lens in diopters (D)
- f is the focal length in meters (m)

### Step-by-Step Solution:

1. **Identify the given power of the lens**:
The power of the lens is given as +5 D.

2. **Use the formula to find the focal length**:
Rearranging the formula \( P = \frac{1}{f} \) gives us:
\[ f = \frac{1}{P} \]

3. **Substitute the value of power into the formula**:
Substitute \( P = 5 \) D into the formula:
\[ f = \frac{1}{5} \]

4. **Calculate the focal length**:
\[ f = \frac{1}{5} = 0.2 \text{ m} \]

5. **Determine the sign of the focal length**:
Since the power is positive (+5 D), the focal length will also be positive. Therefore, the final answer is:
\[ f = +0.2 \text{ m} \]

### Final Answer:
The focal length of the lens is **0.2 meters**.

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