Question

The magnifying power of an astronomical telescope is \( m \). If the focal length of the eyepiece is doubled, the magnifying power will become

• A. \( \frac{m}{4} \)
• B. \( \frac{m}{2} \)
• C. \( 2m \)
• D. \( m \)

Hint:

In telescopes, magnifying power is inversely proportional to the focal length of the eyepiece. Doubling the focal length of the eyepiece halves the magnifying power.

Answer 1

The Correct Option is B

Step 1: Magnifying power of a telescope.
The magnifying power of a telescope is given by: \[ m = \frac{D}{f_e} \] where \( D \) is the aperture of the objective lens and \( f_e \) is the focal length of the eyepiece. If the focal length of the eyepiece is doubled, the magnifying power will be halved.
Step 2: Conclusion.
Thus, when the focal length of the eyepiece is doubled, the new magnifying power will be \( \frac{m}{2} \), which is option (B).