NEET Ray Optics — Set 6

Question 1

A convex mirror of focal length $ 15 \, \text{cm} $ forms an image of an object placed $ 45 \, \text{cm} $ from it. What is the magnification of the image?

Accepted Answer

Focal length: $ f = 15 \, \text{cm} $ (positive for convex mirror). Object distance: $ u = -45 \, \text{cm} $. Mirror equation: $ \frac{1}{v} + \frac{1}{u} = \frac{1}{f} $. $ \frac{1}{v} + \frac{1}{-45} = \frac{1}{15} \Rightarrow \frac{1}{v} = \frac{1}{15} + \frac{1}{45} = \frac{3 + 1}{45} = \frac{4}{45} $. $ v = \frac{45}{4} = 11.25 \, \text{cm} $ (virtual image). Magnification: $ m = -\frac{v}{u} = -\frac{11.25}{-45} = 0.25 $.

Question 2

A convex mirror of focal length $ 10 \, \text{cm} $ forms an image $ 5 \, \text{cm} $ behind the mirror. What is the object distance?

Accepted Answer

Focal length: $ f = 10 \, \text{cm} $ (convex mirror). Image distance: $ v = 5 \, \text{cm} $ (virtual image). Mirror equation: $ \frac{1}{v} + \frac{1}{u} = \frac{1}{f} $. $ \frac{1}{5} + \frac{1}{u} = \frac{1}{10} \Rightarrow \frac{1}{u} = \frac{1}{10} - \frac{1}{5} = \frac{1 - 2}{10} = \frac{-1}{10} $. $ u = -10 \, \text{cm} $.

Question 3

A lens has a power of $ -3 \, \text{D} $. What is its focal length?

Accepted Answer

Power: $ P = \frac{1}{f} $ (in meters). $ P = -3 \, \text{D} \Rightarrow -3 = \frac{1}{f} \Rightarrow f = -\frac{1}{3} \approx -0.333 \, \text{m} \approx -33.3 \, \text{cm} $.

NEET Physics: Ray Optics — Practice Set 6

Q1. A convex mirror of focal length \( 15 \, \text{cm} \) forms an image of an object placed \( 45 \, \text{cm} \) from it. What is the magnification of the image?

Q2. A convex mirror of focal length \( 10 \, \text{cm} \) forms an image \( 5 \, \text{cm} \) behind the mirror. What is the object distance?

Q3. A lens has a power of \( -3 \, \text{D} \). What is its focal length?

Q4. A ray of light passes from air (\( n = 1 \)) to water (\( n = 1.33 \)) at an angle of incidence of \( 35^\circ \). What is the angle of refraction?

Q5. A convex lens (\( f = 25 \, \text{cm} \)) and a concave lens (\( f = 50 \, \text{cm} \)) are in contact. What is the effective focal length?

Q6. What is the critical angle for a diamond-air interface if the refractive index of diamond is \( 2.42 \)?

Q7. A concave lens of focal length \( 12 \, \text{cm} \) has an object placed \( 24 \, \text{cm} \) from it. What is the image distance?

Q8. An object is at a depth of \( 24 \, \text{cm} \) in a medium with refractive index \( 1.6 \). What is the apparent depth?

Q9. What optical property of a prism allows it to be used in binoculars to invert images?

Q10. A glass slab (\( n = 1.5 \)) of thickness \( 9 \, \text{cm} \) is placed over a mark. What is the apparent shift?

Q11. A simple microscope uses a convex lens of focal length \( 5 \, \text{cm} \). What is the magnification when the image is at \( 25 \, \text{cm} \)?

Q12. An object is placed \( 14 \, \text{cm} \) from a convex mirror of focal length \( 28 \, \text{cm} \). What is the magnification?

Q13. An object is placed \( 15 \, \text{cm} \) in front of a concave mirror of focal length \( 10 \, \text{cm} \). Where is the image formed?

Q14. A concave lens has a focal length of \( 20 \, \text{cm} \). Where should an object be placed to get an image half the size of the object?

Q15. What happens to light rays when they strike a convex mirror at an angle parallel to its principal axis?