Question

To increase magnifying power of telescope, we should increase:

• A. the focal length of the objective
• B. the focal length of the eyepiece
• C. aperture of the objective
• D. aperture of the eyepiece

Answer 1

Answer: (A)

the focal length of the objective

Answer 2

Magnifying power of a telescope is $M=\frac{\text { angle subtended by final image at eye }}{\text { angle subtended by the object at eye }}$ When final image is formed at infinity, and $f_{o}$ is focal length of objective, $f_{e}$ is focal length of eye-piece then magnifying power is given by $M=\frac{f_{o}}{f_{e}}$ Since, $M \propto f_{o}$, therefore by increasing focal length of objective we can increase magnifying power.