Question

For a telescope, larger the diameter of the objective lens

• A. greater is the resolving power
• B. smaller is the resolving power
• C. greater is the magnifying power
• D. smaller is the magnifying power

Answer 1

Answer: (A)

The resolving power of a telescope is its ability to show two distant closely lying objects as just separate. The reciprocal of resolving power is the limit of resolution of the telescope.
Limit of resolution $=1.22\frac{\lambda }{d}rad$
where $\lambda$ is wavelength and $d$ the aperture (diameter). Hence, to reduce the limit of resolution of a telescope, we must use objective lens of large aperture $(d)$ . Larger the aperture of the objective lens, smaller the limit of resolution or greater the resolving power of the telescope.