The focal length of a normal eye lens is about

Options

A. 1 mm
B. 2 cm
C. 25 cm
D. 1 m

Explanation

To determine the focal length of a normal eye lens, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Normal Eye Lens**:
- The term "normal eye lens" refers to the eye lens when it is in a relaxed state. This means that the eye muscles are not exerting any force to change the shape of the lens.

2. **Condition for Relaxation**:
- In this relaxed position, the eye is capable of focusing on distant objects, which are considered to be at infinity. When viewing objects at infinity, the eye lens does not need to accommodate (change shape) to focus the light.

3. **Focal Length Definition**:
- The focal length of a lens is the distance from the lens to the point where parallel rays of light converge (the focus). For the human eye, this is the distance from the eye lens to the retina.

4. **Distance from Eye Lens to Retina**:
- In a normal human eye, when relaxed, the distance from the eye lens to the retina is approximately 2 cm. This distance effectively represents the focal length of the eye lens in this relaxed state.

5. **Conclusion**:
- Therefore, the focal length of a normal eye lens is about 2 cm.

### Final Answer:
The focal length of a normal eye lens is approximately **2 cm**.

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