Sec 4 Physics Reflection & Refraction topical questions

Define the angle of incidence and the angle of reflection, and state the law linking them.

State four properties of the image formed by a plane mirror.

State what is meant by total internal reflection.

A ray inside glass (refractive index 1.5) meets a glass-to-air boundary at 20°. Describe what happens to the ray.

Light inside water (refractive index 1.33) strikes the surface at the largest angle for which it can still escape. Calculate that angle.

A ray in air strikes a glass block (n = 1.5) at 45°.

1. (a)Determine the angle at which the ray travels inside the glass.[3]
2. (b)Describe the direction of the refracted ray relative to the incident ray.[1]
3. (c)Determine the speed of the light while it is inside the glass.[2]

An optical-fibre link carries internet data between two cities.

1. (a)Name the effect that traps the light within the core.[1]
2. (b)State the two conditions needed for this effect inside the fibre.[2]
3. (c)Give two reasons why optical fibres outperform copper cables for long-distance communication.[3]

A swimming pool is 1.2 m deep. The water has refractive index 1.33.

1. (a)Calculate the apparent depth of the pool.[3]
2. (b)Explain why the bottom appears shallower than it really is.[2]
3. (c)State and explain whether a ray going from the water into the air at 30° incidence will leave the pool.[1]

A diver shines a torch beam upward toward the water surface.

1. (a)The critical angle for water is 49°. The beam strikes the surface at 55°. Name the effect observed.[1]
2. (b)Explain what a person above the water sees directly above the torch.[2]
3. (c)Describe the path of the beam after the effect in (a).[1]
4. (d)State two natural or everyday observations explained by this effect.[2]

A periscope uses two 45°–45°–90° glass prisms (n = 1.5).

1. (a)Determine the critical angle for the glass.[2]
2. (b)Light enters a prism perpendicular to a slanted-facing vertical side and meets the hypotenuse at 45°. Show, with a calculation, whether total internal reflection occurs.[3]
3. (c)Give two reasons the periscope designer chose prisms over plane mirrors.[3]

A student measures angles for a rectangular glass block and records: i = 30° with r = 19.5°, and i = 50° with r = 30.7°.

1. (a)Calculate the refractive index from each pair of readings.[4]
2. (b)State the conclusion the data support and why plotting sin i against sin r improves the result.[2]
3. (c)Using n = 1.5, find how fast the light travels through the glass.[2]

A step-index optical fibre has a glass core of refractive index 1.48 clad in a material of refractive index 1.44.

1. (a)Explain why the cladding must have a lower refractive index than the core.[2]
2. (b)Calculate the critical angle at the core–cladding boundary.[2]
3. (c)The fibre is bent sharply so that the light meets the boundary at 60° at one wall and 65° at the opposite wall. Comment on the fate of the ray at each wall.[2]
4. (d)State what happens to the signal if the fibre is bent far beyond its minimum bend radius.[2]

A cut diamond (n = 2.4) and a glass imitation (n = 1.5) are compared under a lamp.

1. (a)Calculate the critical angle of each material.[4]
2. (b)Explain, using the critical angles, why the diamond traps light longer inside and flashes more brightly.[3]
3. (c)State one extra condition, besides a small critical angle, that makes a diamond sparkle so strongly.[1]