Refraction — Set 6
Physics · अपवर्तन · Questions 51–60 of 70
The ratio sin i / sin r for a given pair of media is called?
Correct Answer: D. refractive index
For a fixed pair of media, sin i divided by sin r is constant. This constant is the refractive index for that refraction. It is based on Snell’s law.
What is the unit of refractive index?
Correct Answer: B. no unit (dimensionless)
Refractive index is a ratio of two speeds or two sines. Ratios have no physical unit, so refractive index is dimensionless. Its value depends on wavelength and medium.
For normal viewing from air, refractive index of water can be written as?
Correct Answer: C. n = real depth / apparent depth
For near normal viewing, n equals real depth divided by apparent depth. Refraction makes the apparent depth smaller than the real depth. This relation is used in simple depth calculations.
An object is at real depth 24 cm and appears at 18 cm when seen from air. What is the refractive index of the medium?
Correct Answer: C. 1.33
Use n = real depth / apparent depth for near normal viewing. So n = 24/18 = 1.33. A larger n makes objects look more raised.
For light going from medium 1 (denser) to medium 2 (rarer), the critical angle c satisfies?
Correct Answer: C. sin c = n2/n1
At critical angle, the refracted ray makes 90 degrees with the normal. Snell’s law then gives sin c = n2/n1 for n1 greater than n2. This condition is only for denser to rarer travel.
Glass has refractive index 1.6 w.r.t air. What is the critical angle approximately?
Correct Answer: A. 39 degrees
For critical angle, sin c = 1/n for glass to air. With n = 1.6, sin c = 0.625. This gives c about 39 degrees.
Which statement is generally true?
Correct Answer: A. Higher refractive index means higher optical density
Optical density is commonly linked to refractive index for visible light. Higher refractive index usually means light slows down more. Therefore such a medium is called optically denser.
A ray in water (n = 1.33) hits water-air boundary at 45 degrees. What is the refracted angle approximately (no total internal reflection)?
Correct Answer: C. 70 degrees
Use n1 sin i = n2 sin r with n1 = 1.33 and n2 = 1.0. So sin r = 1.33×sin45 ≈ 1.33×0.707 ≈ 0.941, giving r about 70 degrees. Since i is below the critical angle, refraction occurs.
When light goes from air into glass, which statement is correct?
Correct Answer: B. frequency stays same and wavelength decreases
Frequency remains the same because it is fixed by the source. Speed decreases in glass, so wavelength decreases as well. This follows from λ = v/f.
A glass slab of thickness 4 cm (n = 1.5) is used with incidence 30 degrees from air. What is the lateral shift approximately?
Correct Answer: D. 0.77 cm
First find r using sin r = sin30/1.5, giving r about 19.5 degrees. Then use d = t sin(i - r)/cos r, so d ≈ 4×sin10.5/cos19.5 ≈ 4×0.182/0.943 ≈ 0.77 cm. Lateral shift increases with slab thickness and angle of incidence.