How are speed, frequency and wavelength linked?

They satisfy v equals f times lambda, with frequency set by the source and speed by the medium.

What does refractive index mean?

It tells how many times slower light is in the medium than in vacuum, and it is always above 1.

How is the critical angle calculated?

From sin C equal to 1 over n, and it only applies going from a denser to a less dense medium.

Why does frequency not change on refraction?

Frequency comes from the source, and only speed and wavelength change in a new medium.

S5 Physics waves paper 1: speed frequency wavelength and refractive index

2026-11-10

Tutor Prep Guide · S5 Physics Waves and Refraction

Ten items start from v equal to f lambda, then cover period, refractive index, Snell law and the critical angle.

Direct answers　Items 01 to 03 cover speed, wavelength and period, 04 to 06 the refractive index and Snell law, 07 to 09 the critical angle, constant frequency and total internal reflection, and 10 the multiply divide slip.

01　Paper details (check answers afterwards)

Item	Detail
Questions	10
Suggested time	25
Difficulty mix	Foundation 3 · Intermediate 3 · Challenge 3 · Error redo 1
Chapter	Chapter: S5 Physics Waves and Refraction
Level	S5

02　Questions (10 items)

FoundationA wave has frequency 50 Hz and wavelength 2 m. Find its speed.
FoundationSound travels at 340 m/s in air with frequency 170 Hz. Find the wavelength.
FoundationA wave has period 0.02 s. Find its frequency.
IntermediateA medium has refractive index 1.5. Find the speed of light inside it, taking 3 times 10 to the 8 m/s as the vacuum speed.
IntermediateLight travels at 2 times 10 to the 8 m/s in a medium. Find its refractive index.
IntermediateLight enters water of refractive index 1.33 from air at an angle of incidence of 30 degrees. Find the angle of refraction.
ChallengeA medium has refractive index 2.0. Find the critical angle for light going from it into air.
ChallengeWhen light passes from air into glass, which quantity stays unchanged?
ChallengeLight travels from a denser to a less dense medium with an angle of incidence larger than the critical angle. What happens?
Error redoA wave has frequency 250 Hz and wavelength 2 m. A student divides and answers 125 m/s. What is the correct speed?

03　Answers and one-line notes

#	Answer	One-line note
1	100 m/s	Speed equals frequency times wavelength, that is 50 times 2.
2	2 m	Wavelength is speed divided by frequency, that is 340 divided by 170.
3	50 Hz	Frequency is the reciprocal of period, that is 1 divided by 0.02.
4	2 times 10 to the 8 m/s	Refractive index is the vacuum speed divided by the medium speed, so the speed is 3 times 10 to the 8 divided by 1.5.
5	1.5	The index is 3 times 10 to the 8 divided by the speed inside the medium.
6	about 22.1 degrees	Using n1 sin theta1 equal to n2 sin theta2, sin theta2 is sin 30 degrees divided by 1.33.
7	30 degrees	The critical angle comes from sin C equal to 1 divided by n.
8	Frequency	Frequency is set by the source, while speed and wavelength both change in a new medium.
9	Total internal reflection, with no refracted ray	Once the angle exceeds the critical angle the light is entirely reflected back into the first medium.
10	500 m/s	Speed is frequency multiplied by wavelength, not divided, so it is 250 times 2.

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.

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