Refraction — Set 3
Physics · अपवर्तन · Questions 21–30 of 70
A ray goes from air to glass (n = 1.5) with incidence 30 degrees. What is the angle of refraction approximately?
Correct Answer: A. 19 degrees
Use Snell’s law: sin r = sin i / n for air to glass. With i = 30 degrees and n = 1.5, sin r = 0.5/1.5 = 0.333. This gives r about 19 degrees.
What is the critical angle for glass (n = 1.5) to air approximately?
Correct Answer: B. 42 degrees
For critical angle, sin c = 1/n for glass to air. With n = 1.5, sin c = 0.666. This gives c about 42 degrees.
A ray in water (n = 1.33) hits the surface to air at 30 degrees to the normal. What is the refracted angle approximately?
Correct Answer: A. 42 degrees
Use n1 sin i = n2 sin r with n1 = 1.33 and n2 = 1.0. So sin r = 1.33×sin30 = 1.33×0.5 = 0.665. This gives r about 42 degrees.
A pond is 3.0 m deep and refractive index of water is 1.5. What is its apparent depth when viewed from air near normal?
Correct Answer: B. 2.0 m
Apparent depth d' = real depth / n for near normal viewing. So d' = 3.0/1.5 = 2.0 m. Objects in water look raised due to refraction.
Lens maker ideas use refractive index mainly as?
Correct Answer: D. index of lens material relative to surrounding medium
Lens behavior depends on refractive index of lens material relative to the surrounding medium. Refraction happens at both curved surfaces of the lens. Higher relative refractive index generally gives stronger bending.
Dispersion by a prism happens mainly because refractive index?
Correct Answer: D. depends on wavelength (color)
A prism disperses light because refractive index varies with wavelength. Different colors bend by different amounts during refraction. Violet usually bends more than red in common glass.
In ordinary glass, which color generally has the highest refractive index?
Correct Answer: A. Violet
Violet light generally has the highest refractive index in glass. That means violet travels slowest and bends most. This is a part of normal dispersion.
Relative refractive index of medium 2 with respect to medium 1 can be written as?
Correct Answer: A. n21 = v1/v2
Relative refractive index n21 compares medium 2 to medium 1. It can be written as n21 = v1/v2 where v1 and v2 are speeds in the two media. It is also equal to n2/n1.
When light enters a medium of higher refractive index, its speed?
Correct Answer: A. decreases
The correct answer is 'decreases'. Speed of light in a medium is v = c/n. A higher refractive index means a smaller v. This is why denser media bend light more.
In normal dispersion, refractive index generally increases when wavelength?
Correct Answer: C. decreases
In normal dispersion, shorter wavelength light has higher refractive index. So n generally increases as wavelength decreases. This makes violet bend more than red.