Discussion Forum

The limit of resolution of a telescope is $2.5 \times 10^{-7}$ rad. If the  telescope is used to detect light of wavelength  500 nm coming from a star, the diameter of the objective lens used by the telescope is 

Answer:

Explanation:

Given , limit of resolution  , $\alpha= 2.5 \times 10^{-7}$ rad

 and wavelength , $\lambda$=500 nm

 As, limit of resolution of a telescope,

   $\alpha = \frac{1.22 \lambda}{a}$

 So,   $a= \frac{1.22 \lambda}{\alpha}= \frac{ 1.22 \times 500 \times 10^{-9}}{ 2.5 \times 10^{-7}}$

 $\Rightarrow$    a=2.44 m

 = 244 cm

 Hence , the correct option is (a)