What the critical angle is, when total internal reflection occurs, sin c = 1/n, and the periscope, binoculars, optical fibres and endoscopes.
5 narrated scenes. Press play, listen and read along — the points appear as they are explained. Use ‹ Prev / Next › or the scene bar to jump to any scene.
Underwater, if you look up at the right angle the surface becomes a perfect mirror. Optical fibres use the same effect to carry the internet across oceans.
Narration uses your device’s built-in voice. No sound? Switch to “Captions only” — the captions advance on their own.
Increase the angle until the ray is totally reflected.
Copy these into your notebook in your own words — that is how they stick.
Angle of incidence in the denser medium for which the angle of refraction is 90°.
Denser → less dense medium AND angle of incidence > c.
sin c = 1/n.
Glass c ≈ 42°; water c ≈ 49°; diamond c ≈ 24°.
Two right-angled prisms; 45° > c so TIR.
Core + lower index cladding; light carried by repeated TIR.
Binoculars, reflectors, telecommunications, endoscopes.
TIR when going from air into glass.
3 quick games on this lesson. Earn XP and badges as you play — your best score for each game is saved. Games are for practice and do not change your exam readiness. More games in the Physics Arcade.
8 items modelled on real CSEC Paper 1 questions. Choose one answer for each, then check. Aim for 80% or better. Work each item on paper first.
Write full answers, then reveal the mark scheme and tick the points you earned (15 marks in total). Show all your working — method marks count. Your answers are saved on this device.
Question 1 [15 marks]
A ray of light travels inside a glass block of refractive index 1.6 towards a glass–air boundary.
(a) (a) Define the critical angle. [2]
(b) (b) Calculate the critical angle for the glass. [3]
(c) (c) State two conditions for total internal reflection. [2]
(d) (d) A ray strikes the boundary at 50°. Describe what happens to it. [2]
(e) (e) Describe how an optical fibre guides light. [3]
(f) (f) State two uses of optical fibres. [2]
(g) (g) Explain why total internal reflection cannot occur when light goes from air into glass. [1]
Find these in your own past-paper booklets for extra timed practice. Items above are written in the style of these papers; any adapted from a specific question say so.