NEET 2020 Physics Question 168 Solution

Light passing through a circular telescope objective of diameter $$D$$ forms an Airy diffraction pattern consisting of a central bright disc surrounded by dark and bright concentric rings. The angular radius of the first dark ring (Airy disc) defines the angular limit of resolution: $$\Delta\theta = \frac{1.22 \lambda}{D}$$.

- Wavelength of light: $$\lambda = 600\text{ nm} = 600 \times 10^{-9}\text{ m} = 6 \times 10^{-7}\text{ m}$$ - Diameter of telescope objective: $$D = 2\text{ m}$$.

$$\Delta\theta = \frac{1.22 \times (6 \times 10^{-7}\text{ m})}{2\text{ m}} = 1.22 \times 3 \times 10^{-7} = 3.66 \times 10^{-7}\text{ rad}$$.

Matches Option 1 exactly.