Question 10
(a)(i) What is a wavefront?
(ii) A wave passes from medium 1 to medium 2 with velocity v1 and v2 respectively. The absolute refractive indices of media 1 and 2 are n1 and n2 respectively.
(I) State an equation connecting v1, v2, n1 and n2,
(II) Given that n
(b)(i) State the principle of superposition of waves.
(ii) List two conditions necessary for constructive interference of waves to occur.
(iii) State the factor that determines the quality of sound from a musical instrument.
(c)When white light travels from air into glass, blue light is deviated more than red light. Explain why.
Observation
Part (a): Performance was poor. Majority of the candidates attempted but failed to give the correct definition.
Part (b): Performance was fair. Majority of candidates who attempted could not get the correct equation.
Part (c): Performance was fair. Few candidates were able to respond correctly to this question.
The expected responses are:
10.(a) (i) A wavefront
A line or surface passing through an advancing wave on which all the particles are vibrating in phase/step
(b) (i) The principle of superposition of waves
When two or more waves interfere/overlap in space, the resultant disturbance at any point is equal to the algebraic sum of the separate/individual disturbances.
(ii) Conditions necessary for constructive interference of waves to occur
They must
- have the same frequency
- be in phase / have constant phase difference
- be coherent
- (iii) Factor that determines the quality of sound from a musical instrument
- - Overtones/harmonics/waveform
(c) Explanation of why blue light gets deviated more than red light when white light travels from air into glass
The wavelength of red light is greater than that of blue light
Frequency remains constant in glass
The velocity of red light is greater than that of blue light in glass