NEET Ray Optics — Set 20

Question 1

A prism of angle $ 45^\circ $ and refractive index $ 1.6 $ produces what minimum deviation?

Accepted Answer

For a thin prism: $ D_m = (n - 1) A $. $ n = 1.6 $, $ A = 45^\circ $. $ D_m = (1.6 - 1) \times 45 = 0.6 \times 45 = 27^\circ $.

Question 2

A telescope has an objective of focal length $ 150 \, \text{cm} $ and an eyepiece of focal length $ 5 \, \text{cm} $. What is its magnifying power?

Accepted Answer

Magnifying power: $ m = \frac{f_o}{f_e} $. $ f_o = 150 \, \text{cm} $, $ f_e = 5 \, \text{cm} $. $ m = \frac{150}{5} = 30 $.

Question 3

A ray of light passes from air into water ($ n = 1.33 $) at an angle of incidence of $ 45^\circ $. What is the angle of refraction?

Accepted Answer

Snell’s law: $ n_1 \sin i = n_2 \sin r $. Air ($ n_1 = 1 $), water ($ n_2 = 1.33 $), $ i = 45^\circ $. $ 1 \times \sin 45^\circ = 1.33 \times \sin r $. $ \sin 45^\circ = \frac{1}{\sqrt{2}} \approx 0.707 \Rightarrow 0.707 = 1.33 \sin r $. $ \sin r = \frac{0.707}{1.33} \approx 0.532 \Rightarrow r = \sin^{-1}(0.532) \approx 32^\circ $.

NEET Physics: Ray Optics — Practice Set 20

Q1. A prism of angle \( 45^\circ \) and refractive index \( 1.6 \) produces what minimum deviation?

Q2. A telescope has an objective of focal length \( 150 \, \text{cm} \) and an eyepiece of focal length \( 5 \, \text{cm} \). What is its magnifying power?

Q3. A ray of light passes from air into water (\( n = 1.33 \)) at an angle of incidence of \( 45^\circ \). What is the angle of refraction?

Q4. What is the primary reason a concave lens cannot form a real image?

Q5. A prism of refracting angle \( 50^\circ \) has a minimum deviation of \( 25^\circ \). What is the refractive index?

Q6. A ray of light is incident at \( 60^\circ \) on a glass-air interface (refractive index of glass = 1.5). What is the angle of refraction in air?

Q7. A ray of light passes from air (\( n = 1 \)) to glass (\( n = 1.5 \)) at an angle of incidence of \( 45^\circ \). What is the angle of refraction?

Q8. A double convex lens has radii of curvature \( 20 \, \text{cm} \) each and refractive index \( 1.5 \). What is its focal length?

Q9. A convex lens (\( f = 20 \, \text{cm} \)) and a concave lens (\( f = 40 \, \text{cm} \)) are in contact. What is the effective focal length?

Q10. An object is placed \( 8 \, \text{cm} \) from a convex mirror of radius of curvature \( 24 \, \text{cm} \). What is the image distance?