NEET Ray Optics — Set 8

Question 1

A ray of light passes from glass ($ n = 1.62 $) to air at an angle of incidence equal to the critical angle. What is the angle of refraction?

Accepted Answer

Critical angle: $ \sin i_c = \frac{n_2}{n_1} = \frac{1}{1.62} \approx 0.617 $. $ i_c = \sin^{-1}(0.617) \approx 38.1^\circ $. At critical angle, angle of refraction = $ 90^\circ $.

Question 2

What characteristic of a convex mirror makes it suitable for use as a rear-view mirror in vehicles?

Accepted Answer

A convex mirror always produces a virtual, erect, and diminished image, regardless of the object’s position. This provides a wide field of view, allowing drivers to see a larger area behind the vehicle, making it ideal for rear-view mirrors despite the reduced image size.

Question 3

Why does a reflecting telescope often use a secondary mirror in its design?

Accepted Answer

In a reflecting telescope (e.g., Cassegrain design), a secondary mirror redirects the light focused by the primary concave mirror through a hole in the primary mirror to the eyepiece. This allows a compact design with a long focal length, improving magnification and convenience of observation.

NEET Physics: Ray Optics — Practice Set 8

Q1. A ray of light passes from glass (\( n = 1.62 \)) to air at an angle of incidence equal to the critical angle. What is the angle of refraction?

Q2. What characteristic of a convex mirror makes it suitable for use as a rear-view mirror in vehicles?

Q3. Why does a reflecting telescope often use a secondary mirror in its design?

Q4. In a convex mirror, what is the significance of the focal point being behind the mirror?

Q5. A telescope has an objective of focal length \( 120 \, \text{cm} \) and an eyepiece of focal length \( 4 \, \text{cm} \). What is its magnifying power?

Q6. What is the primary reason optical fibers are bent without losing light transmission efficiency?

Q7. A double convex lens of refractive index \( 1.5 \) has radii of curvature \( 15 \, \text{cm} \) and \( -15 \, \text{cm} \). What is its focal length?

Q8. A telescope has an objective of focal length \( 200 \, \text{cm} \) and an eyepiece of focal length \( 10 \, \text{cm} \). What is its magnifying power?

Q9. In a convex lens, why does the image transition from virtual to real as the object moves from inside to outside the focal point?

Q10. In a prism, what condition results in the minimum deviation of light?

Q11. An object is at a depth of \( 16 \, \text{cm} \) in water (\( n = 1.33 \)). What is the apparent depth?

Q12. A ray of light passes from glass (\( n = 1.5 \)) to air at an angle of incidence of \( 40^\circ \). What is the angle of refraction?

Q13. A telescope has an objective of focal length \( 100 \, \text{cm} \) and an eyepiece of focal length \( 5 \, \text{cm} \). What is its magnifying power?

Q14. What is the key optical principle behind the working of a periscope?

Q15. A concave lens of focal length \( 25 \, \text{cm} \) has an object placed \( 50 \, \text{cm} \) from it. What is the image distance?