O-LevelPhysicsWaves5054/22 · Oct/Nov 2018 · Q915 Marks

Both sound and ultrasound are waves that travel in solids, liquids and gases.

(a)State how sound differs from ultrasound.[1]
(b)(i)Sound and ultrasound are longitudinal waves that consist of compressions and rarefactions. Explain what is meant by a wave and describe how a longitudinal wave differs from a transverse wave.[3]
(b)(ii)1Fig. 9.1 represents a longitudinal wave of frequency 25000 Hz travelling in oil. On Fig. 9.1, mark two points at the centre of two different rarefactions and label each one R. [Figure 9.1][1]
(b)(ii)2On Fig. 9.1, draw a double-headed arrow to indicate a distance that is equal to one wavelength of the wave.[1]
(b)(ii)3Measure the length of the arrow drawn on Fig. 9.1 and use it to determine the speed of the wave in oil.[2]
(c)(i)A sound wave travelling in a liquid, passes into air. State what happens to the speed of the sound wave as it enters the air.[1]
(c)(ii)The wave in the liquid travels towards the surface at an angle. Fig. 9.2 shows the centres of the compressions of the sound wave in the liquid. On Fig. 9.2, draw the parts of these compressions that are in the air. [Figure 9.2][3]
(d)Describe, in outline, how ultrasound is used in cleaning.[3]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2018). The mark or mark type is shown in brackets.

[1] frequency of sound wave small(er) or its frequency is less than 20 000 Hz
[1] transmission of energy
[1] (through a medium) with no net movement of medium or by vibrating particles
[1] vibrations parallel (and antiparallel) to wave / energy travel direction or cannot be polarised
[1] two centres of rarefactions labelled R
[1] distance from one point to adjacent identical point indicated (with double-headed arrow)
[1] (v =) fλ or 25 000 × 0.047 / 0.048 / 0.049 or 25 000 × 4.7/4.8/4.9 or 25 000 × 47 /48/49
[1] 1200 m/s
[1] decreases
[1] four / five straight lines in air that touch the compressions still in the liquid and no intermediate / extra lines between the correct lines
[1] at least four compressions in air parallel to each other
[1] at least four straight lines at shallower angle from horizontal and slope correct
[1] object (to be cleaned) immersed in liquid / solvent
[1] object/liquid agitated / vibrated by ultrasound
[1] dirt (particles) shaken off or dislodges / removes dirt

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