Question

Telescope has objective diameter 250 cm. For wavelength \( \lambda = 600 \, \text{nm} \), the limit of resolution is:

• A. \( 1.5 \times 10^{-7} \, \text{rad} \)
• B. \( 2.0 \times 10^{-7} \, \text{rad} \)
• C. \( 3.0 \times 10^{-7} \, \text{rad} \)
• D. \( 4.5 \times 10^{-7} \, \text{rad} \)

Hint:

Use Rayleigh’s criterion \( \theta = \frac{1.22 \lambda}{D} \) for diffraction-limited resolution of telescopes.

Answer 1

The Correct Option is C

Limit of resolution: \( \theta = \frac{1.22 \lambda}{D} \)
\[ \lambda = 600 \times 10^{-9}, D = 2.5 \, \text{m} \Rightarrow \theta = \frac{1.22 \cdot 600 \times 10^{-9}}{2.5} \approx 3.0 \times 10^{-7} \, \text{rad} \]