CAIE A-Level Physics 7 Waves

Practise analysing progressive, transverse and longitudinal waves, speed, intensity, Doppler shifts, electromagnetic spectra, polarisation and filters.

Exam points

interpret wave quantities and graphs and use v = fλ to solve progressive-wave problems
analyse transverse and longitudinal wave behaviour, including graphical representations and phase
explain and calculate Doppler shifts for moving sound sources
classify electromagnetic waves by transverse behaviour, speed, wavelength and spectrum
analyse polarisation and calculate intensity transmission through filters

Covered syllabus points

7.1 Progressive waves 7.2 Transverse and longitudinal waves 7.3 Doppler effect for sound waves 7.4 Electromagnetic spectrum 7.5 Polarisation

[Maximum number: 5]

A progressive transverse wave travelling from left to right is shown at an instant in time in Fig. 4.1.

Fig. 4.1

R and T are points on the wave.

(a)

State the phase difference between the points R and T .
phase difference =

[ 1 ]

$270^{\circ}$

A1

(b)

On Fig. 4.1, draw an arrow at point T to show the direction of movement of point T at the instant shown.

[ 1 ]

(c)

The horizontal distance between R and T is 0.62 cm , as shown in Fig. 4.2.

Fig. 4.2 (not to scale)

The speed of the wave is $0.27 \mathrm{~ms}^{-1}$ .
Calculate the frequency of the wave.
frequency = Hz

[ 3 ]

$v=f \lambda$

or
$v=\lambda / T \text { and } f=1 / T$

C1

$\begin{aligned} \text { wavelength } =0.62 \times 10^{-2} \times(4 / 3) ( \left.=0.83 \times 10^{-2} \mathrm{~m}\right) \end{aligned}$

C1

$\begin{aligned} f =0.27 /\left(0.83 \times 10^{-2}\right) =33 \mathrm{~Hz} \end{aligned}$

A1

[Maximum number: 7]

(a)

Define the frequency of a sound wave.

[ 1 ]

(b)

A sound wave travels through air. Describe the motion of the air particles relative to the direction of travel of the sound wave.

[ 1 ]

(c)

The sound wave emitted from the horn of a stationary car is detected with a microphone and displayed on a cathode-ray oscilloscope (c.r.o.), as shown in Fig. 5.1.

Fig. 5.1

The y-axis setting is $5.0 \mathrm{mV} \mathrm{cm}^{-1}$ .
The time-base setting is $0.50 \mathrm{~ms} \mathrm{~cm}^{-1}$ .

[ 5 ]

(i)

Use Fig. 5.1 to determine the frequency of the sound wave.
frequency = Hz

[ 2 ]

T=2(.0)(ms)

C1

$f=500 \mathrm{~Hz}$

A1

(ii)

The horn of the car sounds continuously. Describe the changes to the trace seen on the c.r.o. as the car travels at constant speed
1. directly towards the stationary microphone,
2. directly away from the stationary microphone.

[ 3 ]

[Maximum number: 3]

A child on a sledge slides down a steep hill and then travels in a straight line up an ice-covered slope, as illustrated in Fig. 3.1.

Fig. 3.1 (not to scale)

The sledge passes point A with speed $18 \mathrm{~ms}^{-1}$ at time t=0 and then comes to rest at point B. The child applies a brake to the sledge at point B. The brake does not keep the sledge stationary and it immediately slides back down the slope towards A .

The variation with time t of the velocity v of the sledge from t=0 to $t=24 \mathrm{~s}$ is shown in Fig. 3.2.

Fig. 3.2

(a)

The child on the sledge blows a whistle between $t=4.0 \mathrm{~s}$ and $t=8.0 \mathrm{~s}$ . The whistle emits sound of frequency 900 Hz . The speed of the sound in the air is $340 \mathrm{~ms}^{-1} . \mathrm{A}$ man standing at point A hears the sound.

Use Fig. 3.2 to

[ 3 ]

(i)

determine the initial frequency of the sound heard by the man,
initial frequency = Hz

[ 2 ]

$f_{0}=(900 \times 340) /(340+12)$

C1

$=870 \mathrm{~Hz}$

A1

(ii)

describe and explain qualitatively the variation, if any, in the frequency of the sound heard by the man.

[ 1 ]

[Maximum number: 1]

An electromagnetic wave is travelling through a vacuum.
What could be the wavelength and period of the electromagnetic wave?

wavelength

period

$1.2 \times 10^{-10} \mathrm{Tm}$

2.5 Ms

1.2 pm

$2.5 \times 10^{11} \mathrm{Gs}$

$1.2 \times 10^{2} \mathrm{pm}$

$4.0 \times 10^{-10} \mathrm{~ns}$

$1.2 \times 10^{3} \mu \mathrm{~m}$

4.0 ns

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Covered syllabus points

7. Waves question 1

Question (a)

Question (b)

Question (c)

7. Waves question 2

Question (a)

Question (b)

Question (c)

Question (i)

Question (ii)

7. Waves question 3

Question (a)

Question (i)

Question (ii)

7. Waves question 4