Geometrical optics

Written by Dr. Hamza Farooq (Physics)

Class 10 · Physics · 10 questions

Name: ____________________ Date: ____________

The speed of light in vacuum is about:
- A 3 x 10⁶ m/s
- B 3 x 10¹⁰ m/s
- C 340 m/s
- D 3 x 10⁸ m/s
A concave mirror is also called a:
- A Prism
- B Plane mirror
- C Converging mirror
- D Diverging mirror
The focal length of a mirror of radius of curvature 20 cm is:
- A 40 cm
- B 10 cm
- C 20 cm
- D 5 cm
Total internal reflection occurs when light goes from:
- A Rare to dense medium
- B Dense to rare medium above the critical angle
- C Air to vacuum
- D Any medium at 0 degrees
A convex lens is used to correct:
- A Long sight
- B Astigmatism only
- C Short sight
- D Colour blindness
The power of a lens of focal length 0.5 m is:
- A 0.5 D
- B 2 D
- C 1 D
- D 5 D
The image formed by a plane mirror is:
- A Real and inverted
- B Virtual and inverted
- C Real and upright
- D Virtual and upright
A convex lens is also called a:
- A Prism
- B Plane lens
- C Converging lens
- D Diverging lens
The bending of light as it passes from one medium to another is:
- A Dispersion
- B Diffraction
- C Reflection
- D Refraction
White light splits into colours in a prism. This is called:
- A Diffraction
- B Polarisation
- C Dispersion
- D Reflection

Answer key

1. D, 2. C, 3. B, 4. B, 5. A, 6. B, 7. D, 8. C, 9. D, 10. C

Light travels at about 3 x 10⁸ m/s in vacuum.
A concave mirror converges parallel rays to a focus.
f = R / 2 = 10 cm.
It needs light travelling from a denser to a rarer medium with an angle of incidence above the critical angle.
Long sight (hypermetropia) is corrected by a converging, convex lens.
Power = 1 / f in metres = 1 / 0.5 = 2 D.
The image appears behind the mirror, laterally inverted.
It brings parallel rays together.
This is refraction.
Different colours bend by different amounts.