When the length of a microscope tube increases, its magnifying power

Options

A. decreases
B. increases
C. does not change
D. becomes zero

Explanation

To solve the question regarding the effect of increasing the length of a microscope tube on its magnifying power, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Magnifying Power Formula**:
The magnifying power (MP) of a microscope can be expressed as:
\[ MP = \frac{V}{U} \cdot \frac{D}{U_e} \]
where:
- \( V \) = distance of the image from the eyepiece,
- \( U \) = distance of the object from the objective,
- \( D \) = near point distance (typically taken as 25 cm for a normal eye),
- \( U_e \) = distance of the image from the eyepiece.

2. **Relate Length of the Microscope Tube to Distances**:
The length \( L \) of the microscope tube is given by:
\[ L = V + U_e \]
If the length \( L \) increases, it implies that either \( V \) or \( U_e \) (or both) must increase.

3. **Analyze the Effect of Increasing Length**:
- When \( L \) increases, and if we assume \( U_e \) remains constant, then \( V \) must increase.
- If \( U \) (the distance of the object) also increases, it means the object is further away from the objective lens.

4. **Evaluate the Magnifying Power**:
- As \( U \) increases, the term \( \frac{V}{U} \) will decrease because \( V \) is not increasing as fast as \( U \).
- Consequently, the overall magnifying power \( MP \) decreases.

5. **Conclusion**:
Therefore, when the length of the microscope tube increases, the magnifying power of the microscope decreases.

### Final Answer:
When the length of a microscope tube increases, its magnifying power decreases.

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