Ray and Wave Optics — Practice

Question 1

A concave mirror has a radius of curvature of 20 cm. Its focal length is:
(a) 10 cm (b) 20 cm (c) 40 cm (d) 5 cm

Accepted Answer

(a) 10 cm.

f = R/2 = 20/2 = 10 cm.

Question 2

The speed of light in a medium is 2 × 10⁸ m/s. The refractive index of the medium is (c = 3 × 10⁸ m/s):
(a) 1.5 (b) 0.67 (c) 2 (d) 1.33

Accepted Answer

(a) 1.5.

n = c/v = 3 × 10⁸ / 2 × 10⁸ = 1.5.

Question 3

The speed of light in a medium of refractive index 1.5 is (c = 3 × 10⁸ m/s):
(a) 2 × 10⁸ m/s (b) 3 × 10⁸ m/s (c) 4.5 × 10⁸ m/s (d) 1.5 × 10⁸ m/s

Accepted Answer

(a) 2 × 10⁸ m/s.

v = c/n = 3 × 10⁸ / 1.5 = 2 × 10⁸ m/s. Light always slows in a denser medium.

Question 4

The critical angle for a medium of refractive index 2 (relative to air) is:
(a) 30° (b) 45° (c) 60° (d) 90°

Accepted Answer

(a) 30°.

sinθc = 1/n = 1/2 = 0.5, so θc = 30°.

Question 5

Total internal reflection occurs when light travels:
(a) from a denser to a rarer medium at an angle greater than the critical angle (b) from a rarer to a denser medium (c) at any angle between two media (d) only in vacuum

Accepted Answer

(a) from a denser to a rarer medium at an angle greater than the critical angle.

TIR requires both conditions: denser → rarer, and incidence beyond the critical angle. It is the basis of optical fibres.

Question 6

The power of a convex lens of focal length 20 cm is:
(a) +5 D (b) +0.05 D (c) +20 D (d) +2 D

Accepted Answer

(a) +5 D.

P = 1/f (in metres) = 1/0.2 = +5 D. A convex lens has positive power.

Question 7

A converging lens is:
(a) convex (b) concave (c) plane (d) always diverging

Accepted Answer

(a) convex.

A convex lens converges parallel light to a real focus (positive power); a concave lens diverges it.

Question 8

Two thin lenses of powers +5 D and +3 D are placed in contact. The power of the combination is:
(a) +8 D (b) +2 D (c) +15 D (d) +1.6 D

Accepted Answer

(a) +8 D.

For lenses in contact powers add: P = P₁ + P₂ = 5 + 3 = 8 D (focal length 1/8 m = 12.5 cm).

Question 9

In a Young's double-slit experiment, λ = 600 nm, slit separation d = 1 mm and screen distance D = 1 m. The fringe width is:
(a) 0.6 mm (b) 6 mm (c) 0.06 mm (d) 1.2 mm

Accepted Answer

(a) 0.6 mm.

β = λD/d = (600 × 10⁻⁹ × 1) / (1 × 10⁻³) = 600 × 10⁻⁶ m = 0.6 mm.

Question 10

Myopia (short-sightedness) is corrected using a:
(a) concave (diverging) lens (b) convex (converging) lens (c) cylindrical lens (d) plane mirror

Accepted Answer

(a) concave (diverging) lens.

A myopic eye converges light too strongly, focusing in front of the retina; a diverging (concave) lens spreads the light first so it focuses on the retina.

Question 11

Hypermetropia (long-sightedness) is corrected using a:
(a) convex (converging) lens (b) concave (diverging) lens (c) bifocal only (d) no lens

Accepted Answer

(a) convex (converging) lens.

A hypermetropic eye converges light too weakly, focusing behind the retina; a converging (convex) lens adds the needed convergence.

Question 12

When white light passes through a prism, the colour that deviates the most is:
(a) violet (b) red (c) green (d) yellow

Accepted Answer

(a) violet.

Violet has the shortest wavelength and the highest refractive index in glass, so it bends (deviates) the most; red deviates the least.

Question 13

In reflection at a plane surface, the angle of incidence is 30°. The angle of reflection is:
(a) 30° (b) 60° (c) 15° (d) 90°

Accepted Answer

(a) 30°.

By the law of reflection, the angle of reflection equals the angle of incidence, both measured from the normal.

Question 14

The phenomenon of polarisation shows that light is:
(a) a transverse wave (b) a longitudinal wave (c) a stream of particles only (d) unable to travel in vacuum

Accepted Answer

(a) a transverse wave.

Only transverse waves can be polarised (restricted to one plane of oscillation); sound, being longitudinal, cannot be polarised. So polarisation is direct evidence that light is transverse.

Question 15

The image formed by a convex mirror of a real object is always:
(a) virtual, erect and diminished (b) real and inverted (c) real and magnified (d) virtual and magnified

Accepted Answer

(a) virtual, erect and diminished.

A convex mirror diverges light, so it always forms a virtual, upright, smaller image — which is why it is used as a wide-view rear-view mirror.

Practice — Ray and Wave Optics

Sign in to save attempts to your dashboard and track your accuracy over time

Find a verified tutor

Join a live course

Browse coaching centres

About

Categories

Support

Documentation

Get Study Tips & Updates

Download Our App

Download for iOS

Download for Android

Popular Cities