A convex lens has mean focal length of 20 cm. The dispersive power of the material of the lens is 0.02. The longitudinal chromatic aberration for an object at infinity is

Options

A. `10^(3)`
B. 0.8
C. 0.4
D. 0.2

Answer

To find the longitudinal chromatic aberration for a convex lens, we can use the formula:

\[ \text{Longitudinal Chromatic Aberration} = \omega \times f \]

where:
- \(\omega\) is the dispersive power of the lens material,
- \(f\) is the focal length of the lens.

### Step-by-Step Solution:

1. **Identify the given values:**
- Focal length (\(f\)) = 20 cm
- Dispersive power (\(\omega\)) = 0.02

2. **Substitute the values into the formula:**
\[ \text{Longitudinal Chromatic Aberration} = \omega \times f = 0.02 \times 20 \]

3. **Perform the multiplication:**
\[ 0.02 \times 20 = 0.4 \]

4. **Conclusion:**
The longitudinal chromatic aberration for the given convex lens is \(0.4\) cm.

### Final Answer:
The longitudinal chromatic aberration for an object at infinity is **0.4 cm**.

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