CAIE A-Level Physics AS 7.1 Progressive Waves Questions

Practise reading wave diagrams and traces, calculating amplitude, phase, frequency, wavelength and speed, and relating progressive-wave energy to intensity.

Exam points

interpret amplitude, phase, period, frequency and wavelength from wave descriptions, graphs or CRO measurements
derive and apply v = fλ to calculate wave speed, frequency or wavelength with consistent units
explain progressive-wave energy transfer and calculate intensity using power, area and amplitude relationships

Covered syllabus points

7.1.1—What is meant by wave motion as illustrated by vibration in ropes, springs 7.1.2—The terms displacement, amplitude, phase difference, period, frequency 7.1.3—The use of the time-base and y-gain of a cathode-ray oscilloscope (CRO) to 7.1.4—The definitions of speed, frequency and wavelength, the wave equation v = f 7.1.5—V = f λ 7.1.6—Energy is transferred by a progressive wave 7.1.7—Intensity = power/area and intensity ∝ (amplitude)2

[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 ]

$270^{\circ}$

(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
$v=\lambda / T \text { and } f=1 / T$ $\begin{aligned} \text { wavelength } =0.62 \times 10^{-2} \times(4 / 3) ( \left.=0.83 \times 10^{-2} \mathrm{~m}\right) \end{aligned}$ $\begin{aligned} f =0.27 /\left(0.83 \times 10^{-2}\right) =33 \mathrm{~Hz} \end{aligned}$

[Maximum number: 1]

A transverse progressive wave on a string has a wavelength of 12 cm and an amplitude of 1.5 cm . The speed of the wave on the string is $48 \mathrm{~cm} \mathrm{~s}^{-1}$ .

What is the distance travelled by a point on the string in a time of 2.0 s ?

12 cm

24 cm

48 cm

$96 \mathrm{~cm}$

[Maximum number: 1]

The diagram shows a representation of a wave on the screen of an oscilloscope.

Figure for Question 3 — CAIE A-Level Physics AS

The y-gain is set to $3.5 \mathrm{mV} \mathrm{cm}^{-1}$ .
What is the amplitude of the wave?

0.57 mV

3.5 mV

7.0 mV

14 mV

[Maximum number: 1]

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.

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

[Maximum number: 1]

A loudspeaker oscillates with frequency f to produce sound waves of wavelength $\lambda$ . The loudspeaker makes N oscillations in time t.

Use your answers in (i) to deduce the equation relating the speed v of the sound wave to f and $\lambda$ .

v(= distance / time $)=N \lambda /(N / f)$ so $v=f \lambda$

[Maximum number: 1]

The range of frequencies of sound waves emitted by blue whales is 10 Hz to 40 Hz .
The speed of sound in seawater is approximately $1.5 \mathrm{~km} \mathrm{~s}^{-1}$ .
What is the approximate range of wavelengths of the sound waves emitted by blue whales?

$6.7 \mathrm{~mm}$ to 27 mm

3.8 cm to 15 cm

$6.7 \mathrm{~m}$ to 27 m

38 m to 150 m

[Maximum number: 1]

Which statement is correct for all types of progressive wave?

The distance from a peak to the next trough is equal to a wavelength.

They can be demonstrated in ripple tanks.

They consist of vibrating atoms.

They transfer energy from one position to another.

[Maximum number: 1]

A plane wave of amplitude A is incident on a surface of area S placed so that it is perpendicular to the direction of travel of the wave. The energy per unit time reaching the surface is E.

The amplitude of the wave is increased to 2 A and the area of the surface is reduced to $\frac{1}{2} S$ .
How much energy per unit time reaches this smaller surface?

4 E

2 E

$\frac{1}{2} E$

All question bank results loaded

Covered syllabus points

Question 1

Question (a)

Question (b)

Question (c)

Question 2

Question 3

Question 4

Question 5

Question 6

Question 7

Question 8