Refraction — Set 4
Physics · अपवर्तन · Questions 31–40 of 70
Refraction of sound in the atmosphere is mainly due to change of?
Correct Answer: D. sound speed with temperature and wind
Sound refraction happens when sound speed changes across layers of air. Temperature and wind gradients change the speed. The wave bends towards the region of lower speed.
At night, distant sounds are often heard more clearly mainly because sound waves?
Correct Answer: D. refract towards the ground
At night, air near the ground is often cooler than air above. This can make sound speed lower near the ground and bend sound waves downward. So sound can travel farther to a listener.
Optical fibers guide light mainly by?
Correct Answer: A. total internal reflection
Optical fibers work because of total internal reflection at the core-cladding boundary. Light stays trapped in the core when incidence exceeds the critical angle. This allows low-loss signal transmission over long distances.
Which device commonly uses optical fiber bundles to transmit images?
Correct Answer: D. endoscope
An endoscope uses optical fibers to carry light and images. Total internal reflection keeps light inside the fibers. It is widely used for viewing inside the body or narrow spaces.
What is the refractive index of vacuum?
Correct Answer: A. 1
Vacuum is the reference medium for absolute refractive index. Speed of light is maximum in vacuum, so n = c/c = 1. Air has refractive index slightly greater than 1.
If n1 and n2 are absolute refractive indices, then relative refractive index of medium 2 w.r.t medium 1 is?
Correct Answer: B. n2/n1
Relative refractive index compares two media directly. It is given by n21 = n2/n1 using absolute indices. It also equals v1/v2 using speeds.
If refractive index of a medium is 1.33, the ratio v/c is approximately?
Correct Answer: B. 0.75
Use n = c/v, so v/c = 1/n. For n = 1.33, v/c ≈ 1/1.33 ≈ 0.75. This shows light is slower in the medium than in vacuum.
When angle of incidence equals the critical angle, the refracted ray makes angle?
Correct Answer: C. 90 degrees with the normal
Critical angle is defined when the refracted ray just grazes the boundary. That means the angle of refraction is 90 degrees with the normal. It is the limiting case before total internal reflection.
If light in a denser medium strikes the boundary at an angle larger than the critical angle, then?
Correct Answer: A. total internal reflection occurs
For i greater than critical angle, refraction into the rarer medium cannot occur. The ray reflects completely back inside the denser medium. This is called total internal reflection.
A ray travels from air into water. In general, it bends?
Correct Answer: C. towards the normal
Water is optically denser than air for visible light. So light slows down in water and bends towards the normal. The closer the incidence is to the normal, the smaller the bending.