NEET Ray Optics — Set 16

Question 1

In optical fibers, what ensures that light remains confined within the core during transmission?

Accepted Answer

In optical fibers, the core has a higher refractive index than the cladding, enabling total internal reflection. When light strikes the core-cladding boundary at an angle greater than the critical angle, it reflects back into the core, ensuring confinement and minimal loss.

Question 2

What is the critical angle for a crown glass ($ n = 1.52 $) to air interface?

Accepted Answer

Critical angle: $ \sin i_c = \frac{n_2}{n_1} $. Crown glass ($ n_1 = 1.52 $), air ($ n_2 = 1 $). $ \sin i_c = \frac{1}{1.52} \approx 0.658 $. $ i_c = \sin^{-1}(0.658) \approx 41.1^\circ $.

Question 3

A telescope has an objective of focal length $ 120 \, \text{cm} $ and an eyepiece of focal length $ 6 \, \text{cm} $. What is its magnifying power?

Accepted Answer

Magnifying power: $ m = \frac{f_o}{f_e} $. $ f_o = 120 \, \text{cm} $, $ f_e = 6 \, \text{cm} $. $ m = \frac{120}{6} = 20 $.

NEET Physics: Ray Optics — Practice Set 16

Q1. In optical fibers, what ensures that light remains confined within the core during transmission?

Q2. What is the critical angle for a crown glass (\( n = 1.52 \)) to air interface?

Q3. A telescope has an objective of focal length \( 120 \, \text{cm} \) and an eyepiece of focal length \( 6 \, \text{cm} \). What is its magnifying power?

Q4. A double convex lens has radii of curvature \( 30 \, \text{cm} \) and \( -30 \, \text{cm} \) with refractive index \( 1.6 \). What is its focal length?

Q5. Why is the image formed by a plane mirror always virtual?

Q6. An object is placed \( 18 \, \text{cm} \) from a convex mirror of focal length \( 12 \, \text{cm} \). What is the image distance?

Q7. A double convex lens of refractive index \( 1.5 \) has radii of curvature \( 18 \, \text{cm} \) and \( -18 \, \text{cm} \). What is its focal length?

Q8. A lens has a power of \( +3 \, \text{D} \). What is its focal length in centimeters?

Q9. A converging beam meets a convex lens (\( f = 20 \, \text{cm} \)) \( 8 \, \text{cm} \) before the convergence point. What is the new image distance?

Q10. A simple microscope uses a lens of focal length \( 8 \, \text{cm} \). What is the magnification when the image is at infinity?