To increase both the resolving power and magnifying power of a telecscope

Options

A. the focal length of the objective has to be increased
B. both the focal length and aperture of the objective has to be increased
C. the wavelength of light has to be decreased
D. the aperture of the objective has to be increased

Answer

B

Explanation

Resolving power of a telescope
`=(1)/(d theta)=(D)/(1.22lamda)`
where `d theta` is the smallest angular separation between two distinct objects whose images are just seen in a telescope as separate and D is the aperture of the objective lens. therefore, to increase resolving power aperture (D) has to be increased.
Magnifying power of a telescope is given by
`M=|(f_(0))/(f_(e))|`, for normal adjustment.
`=|(f_(0))/(f_(e))(1+(f_(e))/(d))|`,
for final image at least distance of distinct vision (d). where `f_(o) and f_(e)` are the focal lengths of the objective and eye-piece respectively.
It is clear from the above expressions that to increase magnifying power, focal length of the objective `(f_(o))` has to be increased.