Refraction — Set 2

Correct Answer: A. total internal reflection in layers of air

A mirage forms because light bends in air layers of different density and can undergo total internal reflection. Hot air near the ground is optically rarer than cooler air above it. This can make the road look like it has water.

Correct Answer: A. absorption in space

The correct answer is 'absorption in space'. Stars twinkle because their light refracts through turbulent layers of the atmosphere. The refractive index of air changes continuously with temperature and density. Planets twinkle less because they appear as extended sources.

Correct Answer: C. refraction, dispersion, and internal reflection

A rainbow forms due to refraction and dispersion when light enters a raindrop. Light also undergoes internal reflection inside the drop. Different colors emerge at different angles because refractive index depends on wavelength.

Correct Answer: D. goes straight without deviation

The correct answer is 'goes straight without deviation'. At normal incidence, the angle of incidence is zero. Snell’s law then gives angle of refraction also zero, so there is no bending. Only speed and wavelength may change across the boundary.

Correct Answer: B. 2.0×10^8 m/s

Use v = c/n for speed in a medium. Putting c = 3.0×10^8 and n = 1.5 gives v = 2.0×10^8 m/s. Higher refractive index means lower speed of light.

Correct Answer: B. 1.6 nm

Wavelength in a medium is λm = λair/n when frequency stays constant. Substituting 600 nm and n = 1.6 gives 600/1.6 = 375 nm. Frequency remains unchanged during refraction.

Correct Answer: C. Higher refractive index generally means optically denser medium

A medium with larger refractive index is generally called optically denser. Light travels slower in an optically denser medium. Optical density is a term based on light behavior, not just mass density.

Correct Answer: D. parallel to the incident ray

In a parallel-sided slab, refraction occurs twice at the two faces. The emergent ray becomes parallel to the incident ray. It is laterally shifted due to the thickness of the slab.

Correct Answer: C. increasing slab thickness

Lateral displacement grows when the slab thickness increases. The ray travels a longer path inside the slab before emerging. For normal incidence, lateral displacement becomes zero.

Correct Answer: A. angle of incidence equals angle of emergence

At minimum deviation, the path of the ray inside the prism is symmetric. This makes the angle of incidence equal to the angle of emergence. Also the refraction angles inside become equal.