NEET Ray Optics — Set 7

Question 1

A concave mirror of focal length $ 8 \, \text{cm} $ has an object placed $ 16 \, \text{cm} $ from it. What is the image distance?

Accepted Answer

Focal length: $ f = -8 \, \text{cm} $ (concave mirror). Object distance: $ u = -16 \, \text{cm} $. Mirror equation: $ \frac{1}{v} + \frac{1}{u} = \frac{1}{f} $. $ \frac{1}{v} + \frac{1}{-16} = \frac{1}{-8} \Rightarrow \frac{1}{v} = \frac{1}{-8} + \frac{1}{16} = \frac{-2 + 1}{16} = \frac{-1}{16} $. $ v = -16 \, \text{cm} $ (real image).

Question 2

A telescope has an objective of focal length $ 180 \, \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 = 180 \, \text{cm} $, $ f_e = 6 \, \text{cm} $. $ m = \frac{180}{6} = 30 $.

Question 3

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

Accepted Answer

Focal length: $ f = -10 \, \text{cm} $ (concave mirror). Image distance: $ v = -20 \, \text{cm} $ (real image, same side as object). 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} $.

NEET Physics: Ray Optics — Practice Set 7

Q1. A concave mirror of focal length \( 8 \, \text{cm} \) has an object placed \( 16 \, \text{cm} \) from it. What is the image distance?

Q2. A telescope has an objective of focal length \( 180 \, \text{cm} \) and an eyepiece of focal length \( 6 \, \text{cm} \). What is its magnifying power?

Q3. A concave mirror of focal length \( 10 \, \text{cm} \) forms an image \( 20 \, \text{cm} \) from the mirror. What is the object distance?

Q4. A glass slab (\( n = 1.5 \)) of thickness \( 15 \, \text{cm} \) is placed over a pin. By how much does the pin appear raised?

Q5. A convex mirror of focal length \( 18 \, \text{cm} \) produces an image \( 6 \, \text{cm} \) behind the mirror. What is the object distance?

Q6. A ray of light is incident from air (\( n = 1 \)) into glass (\( n = 1.5 \)) at \( 30^\circ \). What is the angle of refraction?

Q7. Why does a prism disperse white light into a spectrum of colors?

Q8. A glass slab (\( n = 1.5 \)) of thickness \( 7.5 \, \text{cm} \) is placed over a point. What is the apparent shift?

Q9. A glass slab (\( n = 1.52 \)) of thickness \( 7.6 \, \text{cm} \) is placed over a dot. What is the apparent shift?

Q10. An object is placed \( 10 \, \text{cm} \) from a convex mirror of focal length \( 15 \, \text{cm} \). What is the image distance?

Q11. A lens has a power of \( -4 \, \text{D} \). What is its focal length?

Q12. An object is placed \( 24 \, \text{cm} \) from a concave mirror of focal length \( 12 \, \text{cm} \). What is the image distance?

Q13. A convex lens of focal length \( 25 \, \text{cm} \) forms an image of an object placed \( 50 \, \text{cm} \) from it. What is the image distance?

Q14. A fish is at a depth of \( 40 \, \text{cm} \) in water (\( n = 1.33 \)). What is its apparent depth when viewed from above?

Q15. In a concave mirror, what prevents the formation of an image when the object is placed at the focal point?