NEET Ray Optics — Set 3

Question 1

A converging beam meets a concave lens ($ f = 10 \, \text{cm} $) $ 4 \, \text{cm} $ before the convergence point. What is the new image distance?

Accepted Answer

Object distance: $ u = -4 \, \text{cm} $ (virtual object), $ f = -10 \, \text{cm} $. Lens formula: $ \frac{1}{v} - \frac{1}{-4} = \frac{1}{-10} \Rightarrow \frac{1}{v} + \frac{1}{4} = \frac{1}{-10} $. $ \frac{1}{v} = \frac{1}{-10} - \frac{1}{4} = \frac{-2 - 5}{20} = \frac{-7}{20} $. $ v = -\frac{20}{7} \approx -2.86 \, \text{cm} $ (2.86 cm to the left).

Question 2

A concave mirror has a focal length of $ 12 \, \text{cm} $. An object is placed $ 18 \, \text{cm} $ from it. What is the image distance?

Accepted Answer

Focal length: $ f = -12 \, \text{cm} $ (concave mirror). Object distance: $ u = -18 \, \text{cm} $. Mirror equation: $ \frac{1}{v} + \frac{1}{u} = \frac{1}{f} $. $ \frac{1}{v} + \frac{1}{-18} = \frac{1}{-12} \Rightarrow \frac{1}{v} = \frac{1}{-12} + \frac{1}{18} = \frac{-3 + 2}{36} = \frac{-1}{36} $. $ v = -36 \, \text{cm} $ (real image).

Question 3

A compound microscope has an objective of focal length $ 2 \, \text{cm} $ and eyepiece of focal length $ 4 \, \text{cm} $ with a tube length of $ 16 \, \text{cm} $. What is the magnification at infinity?

Accepted Answer

Objective magnification: $ m_o = \frac{L}{f_o} = \frac{16}{2} = 8 $. Eyepiece magnification: $ m_e = \frac{D}{f_e} = \frac{25}{4} = 6.25 $. Total magnification: $ m = m_o \times m_e = 8 \times 6.25 = 50 $.

NEET Physics: Ray Optics — Practice Set 3

Q1. A converging beam meets a concave lens (\( f = 10 \, \text{cm} \)) \( 4 \, \text{cm} \) before the convergence point. What is the new image distance?

Q2. A concave mirror has a focal length of \( 12 \, \text{cm} \). An object is placed \( 18 \, \text{cm} \) from it. What is the image distance?

Q3. A compound microscope has an objective of focal length \( 2 \, \text{cm} \) and eyepiece of focal length \( 4 \, \text{cm} \) with a tube length of \( 16 \, \text{cm} \). What is the magnification at infinity?

Q4. In a reflecting telescope, why is a concave mirror preferred over a convex lens as the objective?

Q5. A glass slab (\( n = 1.62 \)) of thickness \( 8.1 \, \text{cm} \) is placed over a dot. What is the apparent shift?

Q6. A lens has a power of \( -5 \, \text{D} \). What is its focal length?

Q7. A convex mirror of radius of curvature \( 36 \, \text{cm} \) has an object placed \( 27 \, \text{cm} \) from it. What is the image distance?

Q8. A ray of light passes from air to crown glass (\( n = 1.52 \)) at an angle of incidence of \( 60^\circ \). What is the angle of refraction?

Q9. A concave mirror of focal length \( 9 \, \text{cm} \) has an object placed \( 18 \, \text{cm} \) from it. What is the image distance?

Q10. A convex lens of focal length \( 15 \, \text{cm} \) forms an image at \( 30 \, \text{cm} \) from the lens. What is the object distance?

Q11. A convex lens of focal length \( 20 \, \text{cm} \) forms a real image at \( 60 \, \text{cm} \) from the lens. What is the object distance?

Q12. 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?

Q13. A glass slab (\( n = 1.5 \)) of thickness \( 12 \, \text{cm} \) is placed over a mark. What is the apparent shift?

Q14. A prism of refracting angle \( 40^\circ \) has a minimum deviation of \( 24^\circ \). What is the refractive index?

Q15. A convex lens of focal length \( 12 \, \text{cm} \) forms an image at \( 24 \, \text{cm} \) from the lens. What is the object distance?