Astronomial telescope has two lenses of focal power 0.5D and 20D. Then its magnifying power is:

Options

A. 10
B. 20
C. 80
D. 40

Explanation

To find the magnifying power of the astronomical telescope with the given focal powers, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Focal Powers**:
- The focal power of the first lens (P1) is given as 0.5 D (diopters).
- The focal power of the second lens (P2) is given as 20 D (diopters).

2. **Understand the Formula for Magnifying Power**:
- The magnifying power (M) of an astronomical telescope can be calculated using the formula:
\[ M = \frac{P2}{P1} \]
where P2 is the focal power of the objective lens and P1 is the focal power of the eyepiece lens.

3. **Substitute the Values**:
- Substitute the values of P2 and P1 into the formula:
\[ M = \frac{20 D}{0.5 D} \]

4. **Calculate the Magnifying Power**:
- Perform the division:
\[ M = \frac{20}{0.5} = 40 \]

5. **Conclusion**:
- Therefore, the magnifying power of the astronomical telescope is 40.

### Final Answer:
The magnifying power of the astronomical telescope is **40**.

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