S2 Science: Reflection, Refraction And Dispersion Of Light (Paper 3 (challenge))

S2 Science: Reflection, Refraction and Dispersion of Light (Paper 3 (challenge))

2026-11-14

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Tutor Prep Guide · The law of reflection and plane mirror images, judging refraction direction, prism dispersion and total internal reflection

S2 Science: Reflection, Refraction and Dispersion of Light (Paper 3 (challenge))

This paper deals with the critical angle, the conditions for total internal reflection and its uses, and uses the sine formula to recover an angle of incidence.

Direct answers　Total internal reflection needs light going from a denser to a less dense medium with an angle of incidence beyond the critical angle, which follows from sine c equals one over n.

01　Paper details (check answers afterwards)

Item	Detail
Questions	10
Suggested time	20
Difficulty mix	Foundation 3 · Intermediate 3 · Challenge 3 · Error redo 1
Chapter	Chapter: S2 Science: Reflection, Refraction and Dispersion of Light
Level	S2

02　Questions (10 items)

FoundationLight goes from water of refractive index 1.33 towards air at an angle of incidence of 50 degrees. What happens?
FoundationWhat allows an optical fibre to carry light signals over long distances?
FoundationWhich three optical effects produce a rainbow?
IntermediateGlass has refractive index 1.5. What is its critical angle?
IntermediateDiamond has refractive index 2.42. What is its critical angle and why does it sparkle?
IntermediateWhich two conditions are needed for total internal reflection?
ChallengeLight travels in glass at an angle of refraction of 30 degrees with refractive index 1.5. What is the angle of incidence?
ChallengeWhite light strikes glass at 45 degrees with red at refractive index 1.51 and violet at 1.53. Which is refracted less and by how much do they differ?
ChallengeA mirage appears on a hot road. Which optical effect causes it?
Error redoA student says total internal reflection happens when light goes from air into water. What is wrong?

03　Answers and one-line notes

#	Answer	One-line note
1	Total internal reflection, so the light stays in the water	The critical angle of water is about 48.8 degrees and 50 degrees is beyond it.
2	Total internal reflection	The light keeps reflecting inside the core at the boundary with the cladding and hardly leaks out.
3	Refraction, dispersion and internal reflection	Sunlight is refracted and dispersed on entering a droplet, reflected inside it, then refracted again on the way out.
4	About 41.8 degrees	The sine of the critical angle is 1 divided by 1.5, which gives about 41.8 degrees.
5	About 24.4 degrees; the small critical angle traps light so it reflects internally many times before leaving.	A larger refractive index gives a smaller critical angle.
6	Light must travel from a denser to a less dense medium and the angle of incidence must exceed the critical angle	Both conditions are required, and reversing the direction removes the effect entirely.
7	About 48.6 degrees	Multiply sin 30 degrees by 1.5 to get 0.75, whose angle is about 48.6 degrees.
8	Violet has the smaller angle of refraction, and they differ by about 0.4 degrees	The angles of refraction are about 27.9 and 27.5 degrees, so violet is deviated more.
9	Total internal reflection between layers of air	Air near the ground is heated and less dense, so light curves upward and reflects totally, looking like water.
10	The direction is reversed: total internal reflection needs light going from a denser to a less dense medium, such as water into air.	Reversing the two media is the most common mistake in this chapter.

04　What to do after marking

After marking, redo only the wrong items and write down which step went wrong (formula, unit, or misread number).
Repeat the same item two days later; move to the next paper only when both attempts are correct.
Parents only need the answer and note columns; there is no need to explain every item.

For light questions ask three things: whether angles are measured from the normal, whether light goes from a denser to a less dense medium or the other way, and how many refractions occur.Tutor Registration →

Questions and answers are written originally by the TutorZone team and are not taken from any school, publisher or examination authority paper. Every value is checked by computer.