NEET Ray Optics — Set 11

Question 1

A convex lens of focal length $ 10 \, \text{cm} $ forms an image at $ 20 \, \text{cm} $ from the lens. What is the object distance?

Accepted Answer

Focal length: $ f = 10 \, \text{cm} $. Image distance: $ v = 20 \, \text{cm} $ (real image). Lens formula: $ \frac{1}{v} - \frac{1}{u} = \frac{1}{f} $. $ \frac{1}{20} - \frac{1}{u} = \frac{1}{10} \Rightarrow \frac{1}{u} = \frac{1}{20} - \frac{1}{10} = \frac{1 - 2}{20} = \frac{-1}{20} $. $ u = -20 \, \text{cm} $.

Question 2

A concave mirror of radius of curvature $ 20 \, \text{cm} $ forms an image $ 20 \, \text{cm} $ from the mirror. What is the object distance?

Accepted Answer

Focal length: $ f = \frac{R}{2} = \frac{-20}{2} = -10 \, \text{cm} $ (concave mirror). Image distance: $ v = -20 \, \text{cm} $ (real image). Mirror equation: $ \frac{1}{v} + \frac{1}{u} = \frac{1}{f} $. $ \frac{1}{-20} + \frac{1}{u} = \frac{1}{-10} \Rightarrow \frac{1}{u} = \frac{1}{-10} + \frac{1}{20} = \frac{-2 + 1}{20} = \frac{-1}{20} $. $ u = -20 \, \text{cm} $.

Question 3

A ray of light passes from water ($ n = 1.33 $) to air at an angle of incidence of $ 50^\circ $. What happens?

Accepted Answer

Critical angle: $ \sin i_c = \frac{n_2}{n_1} = \frac{1}{1.33} \approx 0.752 \Rightarrow i_c \approx 48.75^\circ $. Since $ i = 50^\circ > i_c $, total internal reflection occurs.

NEET Physics: Ray Optics — Practice Set 11

Q1. A convex lens of focal length \( 10 \, \text{cm} \) forms an image at \( 20 \, \text{cm} \) from the lens. What is the object distance?

Q2. A concave mirror of radius of curvature \( 20 \, \text{cm} \) forms an image \( 20 \, \text{cm} \) from the mirror. What is the object distance?

Q3. A ray of light passes from water (\( n = 1.33 \)) to air at an angle of incidence of \( 50^\circ \). What happens?

Q4. An object of height \( 3 \, \text{cm} \) is placed \( 20 \, \text{cm} \) from a concave mirror of focal length \( 15 \, \text{cm} \). What is the height of the image?

Q5. A light ray passes from water (\( n = 1.33 \)) to glass (\( n = 1.5 \)) at an angle of incidence of \( 30^\circ \). What is the angle of refraction?

Q6. A concave mirror has a radius of curvature of \( 40 \, \text{cm} \). An object of height \( 2 \, \text{cm} \) is placed \( 30 \, \text{cm} \) in front of it. What is the height of the image formed?

Q7. An object is at a depth of \( 26.6 \, \text{cm} \) in a medium with refractive index \( 1.33 \). What is the apparent depth?

Q8. What is the critical angle for a dense flint glass (\( n = 1.62 \)) to air interface?

Q9. A compound microscope has an objective of focal length \( 1 \, \text{cm} \) and eyepiece of focal length \( 4 \, \text{cm} \) with a tube length of \( 14 \, \text{cm} \). What is the magnification at infinity?

Q10. A concave lens of focal length \( 20 \, \text{cm} \) forms an image \( 8 \, \text{cm} \) from the lens. What is the object distance?

Q11. An object is placed \( 12 \, \text{cm} \) from a convex mirror of focal length \( 18 \, \text{cm} \). What is the image distance?

Q12. A prism of angle \( 50^\circ \) and refractive index \( 1.4 \) produces what minimum deviation?