The power of a lens is 4 diopter. It is

Options

A. Concave lens of 25 m focal length
B. Convex lens of.35 m focal length
C. Concave lens of 1 m focal length
D. Concave lens of 2 m focal length

Explanation

To solve the question regarding the power of a lens being 4 diopters, we need to understand the relationship between the power of a lens and its focal length.

### Step-by-Step Solution:

1. **Understanding Power of a Lens**:
The power (P) of a lens is defined as the reciprocal of its focal length (f) in meters. The formula is given by:
\[ P = \frac{1}{f} \]
where P is in diopters (D) and f is in meters (m).

2. **Given Information**:
We are given that the power of the lens is 4 diopters. Therefore, we can set up the equation:
\[ 4 = \frac{1}{f} \]

3. **Calculating Focal Length**:
To find the focal length (f), we can rearrange the equation:
\[ f = \frac{1}{P} = \frac{1}{4} \]
This gives us:
\[ f = 0.25 \text{ meters} \]

4. **Identifying the Type of Lens**:
- A lens with a positive focal length (f > 0) is a **convex lens**.
- A lens with a negative focal length (f < 0) is a **concave lens**.
Since the focal length we calculated is positive (0.25 m), this indicates that the lens is a **convex lens**.

5. **Conclusion**:
Therefore, the lens with a power of 4 diopters is a **convex lens with a focal length of 0.25 meters**.

### Final Answer:
The power of a lens is 4 diopters. It is a **convex lens with a focal length of 0.25 meters**.