Question

Assume that the light of wavelength is $ 6000\,\mathring{A} $ coming from a star. What is the time resolution of a telescope whose objective has a diameter of $ 100 $ inch?

• A. $ 3.66 \times 10^{-7} $ rad
• B. $ 1.44 \times 10^{-7} $ rad
• C. $ 2.9 \times 10^{-7} $ rad
• D. $ 5.8 \times 10^{-7} $ rad

Answer 1

Answer: (C)

Given, $\lambda=6000\,\mathring{A}$
$=6\times 10^{-7}\,m$
Diameter of objective lens, $a = 100$ inch
$a=254\,cm$ $(\because$ 1 inch=254 cm)
$=2.54\,m$
Since, we know that
Resolution limit of a telescope
$d\theta=\frac{1.22\lambda}{a}$
$=\frac{1.22\times6\times10^{-7}}{2.54}$
$=2.88\times 10^{-7}$
$=2.9\times 10^{-7}$ rad