Question

A telescope is used to resolve two stars separated by $3.2 \times 10^{-6}$ rad. If the wavelength of light used in $5600\, \mathring{A}$, what should be the aperture of the objective of the telescope?

• A. 0.2135 m
• B. 0.1488 m
• C. 0.567 m
• D. 1 m

Answer 1

Answer: (A)

Aperture of the telescope
$D=\frac{1.22 \lambda}{d \theta}$
Here $\lambda=5600\,\mathring{A}=5600 \times 10^{-10} m , d \theta=3.2 \times 10^{-6} rad$
$\therefore D=\frac{1.22 \times 5600 \times 10^{-10}}{3.2 \times 10^{-6}}$
$\Rightarrow D=0.2135\, m$