Refraction and total internal reflection — return questions

1. define / describe / state / calculate

(a) Define the angle of refraction. (b) Describe what happens to a ray of light that passes from air into glass along the normal. (c) In an experiment, a pupil traces a ray of light through a triangular glass prism on paper. State whether the ray that leaves is parallel to the ray that went in, and give the reason. (d) Supplement. A ray in air enters a block of clear plastic of refractive index 1.42. The angle of refraction is 24°. Calculate the angle of incidence.

(a) The angle of refraction

(b) Along the normal

(c) The ray out of a prism

(d) Supplement: the angle of incidence

2. state / explain / calculate

(a) State the meaning of the critical angle. (b) State the two conditions needed for total internal reflection. (c) The back of a bicycle reflector is a pattern of tiny plastic prisms, with air behind them and no silver layer. Light from a car’s headlights goes into the reflector and is sent back towards the car. Explain how the prisms send the light back. (d) Supplement. A clear plastic has a critical angle of 39°. The speed of light in air is 3.0 × 10⁸ m/s. Calculate the refractive index of the plastic and the speed of light in it. (e) Supplement. A doctor guides an endoscope, a bundle of optical fibres, down into a patient’s stomach, and it bends gently on the way. Explain why light from a lamp at the outside end still reaches the far end.

(a) The critical angle

(b) The two conditions

(c) The bicycle reflector

(d) Supplement: the refractive index and the speed

(e) Supplement: light in an endoscope