Refraction — Set 5
Physics · अपवर्तन · Questions 41–50 of 70
A pencil partially dipped in water looks bent mainly due to?
Correct Answer: C. refraction at the water-air surface
The pencil looks bent because rays from the submerged part refract at the water-air boundary. The apparent position of the underwater part shifts upward. This is a common example of refraction in daily life.
For light going from air to a medium, refractive index of the medium can be found by?
Correct Answer: D. n = sin i / sin r
For air to a medium, Snell’s law gives n = sin i / sin r. This holds for the same wavelength and uniform media. It is a practical way to measure refractive index.
A coin appears to be at 15 cm depth in water. If refractive index of water is 1.25, what is the real depth?
Correct Answer: C. 18.75 cm
For normal viewing, n = real depth / apparent depth. So real depth = n × apparent depth = 1.25×15 = 18.75 cm. Real depth is always greater than apparent depth when viewed from air.
A medium has refractive index 1.25 w.r.t air. What is the critical angle for light going from this medium to air approximately?
Correct Answer: B. 53 degrees
For critical angle, sin c = 1/n for denser to rarer. With n = 1.25, sin c = 0.8. This gives c about 53 degrees.
For a prism at minimum deviation, which relation is correct?
Correct Answer: A. r1 = r2 = A/2
At minimum deviation, the refraction inside the prism is symmetric. So r1 equals r2 and their sum equals the prism angle A, giving r1 = r2 = A/2. This condition is used to find refractive index of prism material.
The formula for refractive index of a prism at minimum deviation is?
Correct Answer: C. n = sin((A+Dm)/2)/sin(A/2)
At minimum deviation, prism refractive index is n = sin((A+Dm)/2)/sin(A/2). It uses prism angle A and minimum deviation Dm. This relation comes from Snell’s law at both faces.
A prism has angle A = 60 degrees and minimum deviation Dm = 40 degrees. What is its refractive index approximately?
Correct Answer: C. 1.53
Use n = sin((A+Dm)/2)/sin(A/2). Here (60+40)/2 = 50 degrees and A/2 = 30 degrees, so n = sin50/sin30. This gives n ≈ 0.766/0.5 ≈ 1.53.
In a rectangular glass slab, lateral displacement becomes zero when?
Correct Answer: B. angle of incidence is 0 degrees
Lateral displacement depends on the bending inside the slab. At normal incidence, the ray goes straight and no shift occurs. So lateral displacement becomes zero when i = 0 degrees.
A ray travels from water to air. In general, it bends?
Correct Answer: B. away from the normal
When light goes from denser to rarer medium, it speeds up. So it bends away from the normal in general. If the incidence exceeds critical angle, total internal reflection occurs.
Which statement about apparent depth is correct for an object in water seen from air near normal?
Correct Answer: C. Apparent depth is less than real depth
Apparent depth is less than real depth when viewed from a rarer medium. This is due to refraction at the interface. The relation is n = real depth / apparent depth for near normal viewing.