Optics and Spectrum Quiz

If a person with uncorrected myopia tries to watch a distant object, what changes occur in their eye to attempt to focus?

1. The ciliary muscles contract, making the lens more convex.
2. The ciliary muscles relax, increasing the focal length of the eye lens.
3. The lens remains highly curved, causing excessive convergence of light.
4. The pupil dilates to allow more light for better focus.

Answer: (c) The lens remains highly curved, causing excessive convergence of light.

A ray of light is incident at an angle of 45° on one face of a prism angle of 30° (n = √2). If the light exits normally from the other face of the prism, what is the angle of deviation?

1. 10°
2. 15°
3. 20°
4. 25°

Answer: (b) 15°

A convex and a concave lens are kept in contact, forming a lens system with a focal length of 40 cm. If the magnitudes of their powers are in the ratio 3:2, what are the focal lengths of the individual lenses?

1. 10 cm, -30 cm
2. 12.5 cm, -25 cm
3. 15 cm, -22.5 cm
4. 13.3 cm, -20 cm

Answer: (d) 13.3 cm, -20 cm

A thin convex lens of focal length 15 cm is placed 5 cm away from a concave lens of focal length 30 cm. If a parallel beam of light is incident on the convex lens, where will the final image be formed?

1. 10 cm behind the concave lens
2. 15 cm behind the concave lens
3. 20 cm behind the concave lens
4. 25 cm behind the concave lens

Answer: (b) 15 cm behind the concave lens

A ray of light enters a 45°-90°-45° prism perpendicularly at one face and undergoes total internal reflection inside the prism. If the refractive index of the material is 2, what is the minimum angle of incidence for total internal reflection inside the prism?

1. 30°
2. 45°
3. 60°
4. 90°

Answer: (b) 45°

A convex lens forms an image three times the size of the object. If the focal length of the lens is 20 cm, what is the object distance?

1. 10.34 cm
2. 12.5 cm
3. 13.34 cm
4. 14.56 cm

Answer: (c) 13.34 cm

The absolute index of refraction for a substance is 2.0 for light having a wavelength of 5.9 × 10–7 metre. In this substance, what is the critical angle for light incident on a boundary with air?

1. 30°
2. 45°
3. 60°
4. 90°

Answer: (a) 30°

A mirror is tilted by 15° from its initial position while keeping the incident ray direction unchanged. If the angle of incidence before tilting was 25°, what is the total deviation of the reflected ray from its original direction?

1. 30°
2. 45°
3. 60°
4. 90°

Answer: (a) 30°

A ray of light travels from air into a glass block as shown. It makes an angle of 60o with the surface of the block. If the refractive index of the glass is 2, what is the angle of refraction?

1. 14.5°
2. 30.5°
3. 43.5°
4. 38.5°

Answer: (a) 14.5°

Assertion (A): A concave mirror can never form an image smaller than the object. Reason (R): The magnification of a concave mirror is always greater than or equal to 1. Choose the correct option:

1. Both A and R are true, and R is the correct explanation of A.
2. Both A and R are true, but R is not the correct explanation of A.
3. A is false, but R is true.
4. A is false, and R is false.

Answer: (d) A is false, and R is false.