An astronomical telescope consists of two convex lenses of focal lengths 20 cm and 4 cm. For the nomal adjustment of the telescope, what is the angular magnification produced by the telescope ?

Options

A. 4
B. 5
C. 6
D. 2

Explanation

To find the angular magnification produced by an astronomical telescope with two convex lenses, we can follow these steps:

### Step 1: Identify the focal lengths
Let:
- Focal length of the objective lens (F₀) = 20 cm
- Focal length of the eyepiece lens (Fₑ) = 4 cm

### Step 2: Understand the formula for angular magnification
The angular magnification (M) of an astronomical telescope in normal adjustment is given by the formula:
\[ M = \frac{F₀}{Fₑ} \]

### Step 3: Substitute the values into the formula
Now, substituting the values of the focal lengths into the formula:
\[ M = \frac{20 \, \text{cm}}{4 \, \text{cm}} \]

### Step 4: Calculate the magnification
Calculating the above expression:
\[ M = \frac{20}{4} = 5 \]

### Conclusion
The angular magnification produced by the telescope is 5.

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