C.2 Wave model
Practice exam-style IB Physics questions for Wave model, aligned with the syllabus and grouped by topic.
Question 1
A pulse travels along a stretched rope from left to right. What is transferred by the pulse?
A.
Both energy and rope material along the rope
B.
Neither energy nor rope material along the rope
C.
Energy, with no net transfer of rope material
D.
Rope material, with no transfer of energy
Question 2
A sound wave travels through air in the positive x-direction. What is the direction of oscillation of the air molecules?
A.
In circular paths around the x-axis
B.
In the x-direction with a net drift at the wave speed
C.
Parallel to the x-direction
D.
Perpendicular to the x-direction only
Question 3
A water wave has frequency 2.5 Hz and wavelength 0.80 m. What is the wave speed?
A.
3.1 m s⁻¹
B.
2.0 m s⁻¹
C.
20 m s⁻¹
D.
0.32 m s⁻¹
Question 4
At the centre of a compression in a sound wave travelling in air, what is true of the pressure variation and the particle displacement from equilibrium?
A.
Both pressure variation and particle displacement maximum
B.
Pressure variation maximum; particle displacement zero
C.
Pressure variation zero; particle displacement maximum
D.
Both pressure variation and particle displacement zero
Question 5
What is the order of electromagnetic radiation from longest wavelength to shortest wavelength?
A.
Radio, infrared, microwave, visible, ultraviolet, gamma rays, X-rays
B.
Radio, microwave, infrared, visible, ultraviolet, X-rays, gamma rays
C.
Visible, infrared, microwave, radio, ultraviolet, X-rays, gamma rays
D.
Gamma rays, X-rays, ultraviolet, visible, infrared, microwave, radio
Question 6
What is a difference between a mechanical wave and an electromagnetic wave?
A.
A mechanical wave transfers matter; an electromagnetic wave transfers energy.
B.
A mechanical wave requires a material medium; an electromagnetic wave can travel in a vacuum.
C.
A mechanical wave has frequency; an electromagnetic wave has no frequency.
D.
A mechanical wave must be transverse; an electromagnetic wave must be longitudinal.
Question 7
A pulse travels along a horizontal spring.
Outline what is meant by a travelling wave.
[1]
State how the motion of the coils differs for a transverse pulse and a longitudinal pulse.
[1]
Question 8
Electromagnetic radiation travels in a vacuum.
State the speed of electromagnetic waves in a vacuum.
[1]
State what oscillates in an electromagnetic wave.
[1]
Question 9
A displacement–time graph for one particle in a wave shows that the time between successive maximum positive displacements is 0.040 s. What is the frequency of the wave?
A.
25 Hz
B.
4.0 Hz
C.
40 Hz
D.
0.040 Hz
Question 10
An electromagnetic wave in a vacuum has wavelength 6.0 × 10⁻⁷ m. What is its frequency?
A.
1.8 × 10² Hz
B.
2.0 × 10⁻¹⁵ Hz
C.
1.8 × 10¹⁵ Hz
D.
5.0 × 10¹⁴ Hz
Question 11
A source emits 12 complete cycles of a wave into a medium. The frequency is 40 Hz and the wave speed is 8.0 m s⁻¹. What is the length of the wave train?
A.
4.8 m
B.
2.4 m
C.
60 m
D.
0.20 m
Question 12
Light enters glass from air. The frequency remains unchanged while the speed decreases. What happens to the wavelength?
A.
It increases because λ = f/v.
B.
It becomes zero because light needs a medium in glass.
C.
It decreases because λ = v/f.
D.
It remains unchanged because frequency is unchanged.
Question 13
A wave on a rope has wavelength 0.45 m and frequency 6.0 Hz.
Calculate the period of oscillation.
[1]
Calculate the wave speed.
[1]
Question 14
The graph shows displacement against time for one particle in a wave.
State the quantity represented by the maximum displacement from the equilibrium line.
[1]
Determine the period from the graph.
[1]
Explain why the wavelength cannot be determined from this graph alone.
[1]
Question 15
A loudspeaker produces a steady sound in air.
State the type of mechanical wave produced in the air.
[1]
Explain why the air is not transported from the loudspeaker to a listener.
[1]
Question 16
Distinguish between a mechanical wave and an electromagnetic wave in terms of:
the physical quantity that oscillates.
[1]
whether a vacuum can support the wave.
[1]
Question 17
The graph shows the displacement of particles in a string against position at one instant for a travelling wave.
Determine the amplitude of the wave.
[1]
Determine the wavelength of the wave.
[1]
The frequency is 12 Hz. Calculate the wave speed.
[1]
Question 18
The diagram represents a longitudinal wave in a spring at one instant.
Identify one labelled compression.
[1]
Identify one labelled rarefaction.
[1]
State the direction of oscillation of the coils relative to the direction of wave travel.
[1]
Explain why the diagram does not show a net transport of the spring along the wave.
[1]
Question 19
A transverse wave travels to the right. At an instant, a point on the string is on a section of the displacement–distance graph with positive gradient. What is the instantaneous direction of motion of this point?
A.
Upwards
B.
To the right
C.
Momentarily at rest
D.
Downwards
Question 20
A longitudinal displacement–distance graph is drawn for a wave travelling to the right. Positive displacement means particles are displaced to the right. At which position is the centre of a compression?
A.
At a maximum negative displacement
B.
At a zero crossing where the graph changes from negative to positive displacement as distance increases
C.
At a maximum positive displacement
D.
At a zero crossing where the graph changes from positive to negative displacement as distance increases
Question 21
Two points on a travelling wave are separated by 0.75λ along the direction of propagation. What is their phase difference?
A.
π/4 rad
B.
π/2 rad
C.
2π rad
D.
3π/2 rad
Question 22
A loudspeaker emits a sound of constant frequency in still air. A microphone is moved directly away from the loudspeaker until its oscilloscope trace is next in phase with the trace from a fixed microphone. The microphone has moved 0.68 m. The frequency is 500 Hz. What is the speed of sound?
A.
735 m s⁻¹
B.
1000 m s⁻¹
C.
170 m s⁻¹
D.
340 m s⁻¹
Question 23
A point source emits electromagnetic radiation uniformly with power P. The intensity at distance r is I. What is the intensity at distance 3r, assuming no absorption?
A.
I/9
B.
I/3
C.
9I
D.
3I
Question 24
A radio transmitter and an ultrasound probe both send waves carrying information. Which comparison is correct?
A.
Both require a material medium because both carry information.
B.
Radio waves can travel through a vacuum; ultrasound requires a material medium.
C.
Both are longitudinal pressure waves in air.
D.
Ultrasound can travel through a vacuum; radio waves require air.
Question 25
A student stands 85 m from a large wall and claps once. The echo is heard 0.50 s after the clap.
State the distance travelled by the sound before the echo is heard.
[1]
Calculate the speed of sound.
[1]
Suggest one reason why a larger wall distance improves this method.
[1]
Question 26
A lamp may be modelled as a point source emitting electromagnetic radiation uniformly in all directions.
State the relationship between intensity I and distance r from the source.
[1]
Explain the physical reason for this relationship.
[1]
State one condition under which this model may not apply well.
[1]
Question 27
A transverse wave travels to the right along a string. A displacement–distance graph at one instant is shown.
Identify one labelled point at which the particle is momentarily at rest.
[1]
State the direction of motion of the particle at a labelled point where the graph has negative gradient.
[1]
Explain your answer to (b).
[1]
Question 28
A longitudinal displacement–distance graph for a wave in a spring is shown. Positive displacement is to the right.
Identify whether point P is a compression or a rarefaction.
[1]
Explain how the displacement of neighbouring coils shows this.
[1]
Question 29
A source emits a wave for 0.80 s into a medium. The wave speed is 12 m s⁻¹ and the frequency is 5.0 Hz.
Calculate the length of the wave train.
[1]
Calculate the wavelength.
[1]
Determine the number of complete cycles in the wave train.
[1]
Question 30
Two microphones connected to an oscilloscope are used to determine the speed of sound. A loudspeaker is driven by a signal generator of known frequency.
Describe how the wavelength can be obtained using the two microphone traces.
[1]
Explain why measuring several wavelengths improves the result.
[1]
State how the speed of sound is then calculated.
[1]
Question 31
A radio wave has frequency 95 MHz.
Calculate its wavelength in vacuum.
[1]
State why this wave can travel from a satellite to Earth through space.
[1]
Question 32
A student says: “X-rays are just very fast visible light.”
State one feature X-rays and visible light have in common.
[1]
State one difference between X-rays and visible light.
[1]
Explain why the phrase “very fast” is misleading.
[1]
Question 33
A student records the sound from a loudspeaker using two microphones. The table gives the separation of the microphones when their oscilloscope traces are in phase for a constant-frequency sound.
| In-phase setting | Microphone separation / m |
|---|---|
| 1 | 0.344 |
| 2 | 0.687 |
| 3 | 1.031 |
| 4 | 1.374 |
| 5 | 1.718 |
| 6 | 2.060 |
Determine the mean separation between successive in-phase positions.
[1]
State what this mean separation represents.
[1]
The signal generator frequency is known. Explain how the speed of sound is found.
[1]
Suggest why using several in-phase positions is better than using one pair of positions.
[1]
Question 34
The graph shows approximate wavelength ranges for regions of the electromagnetic spectrum.
Identify the region containing radiation of wavelength 10⁻² m.
[1]
Identify the region with the shortest wavelengths shown.
[1]
Calculate the frequency of radiation of wavelength 5.0 × 10⁻⁷ m in vacuum.
[1]
State why all regions shown are classified as electromagnetic waves.
[1]
Question 35
A sensor measures the intensity of light from a small lamp at different distances. The graph shows the variation of intensity with distance.
Describe how the intensity changes as distance increases.
[1]
Use the graph to determine whether doubling the distance approximately quarters the intensity.
[1]
Explain why this behaviour is expected for a point source.
[1]
Question 36
Two points A and B on a sinusoidal travelling wave are separated by 0.30 m. The wavelength is 0.80 m.
Determine the phase difference between A and B in radians.
[1]
State whether A and B are in phase, in antiphase, or neither.
[1]
State the separation between two nearest points that are in antiphase.
[1]
Question 37
A small transmitter radiates power uniformly. A receiver measures intensity I at a distance of 20 m.
Predict the intensity at 50 m in terms of I.
[1]
State two assumptions made in using this prediction.
[1]
Question 38
A sequence of displacement–distance graphs shows a transverse wave on a string at equal time intervals.
Determine the direction of propagation of the wave pattern.
[1]
Determine the speed of the wave pattern.
[1]
For the labelled particle P, state its direction of motion at the first instant shown.
[1]
Explain why P does not have the speed found in (b).
[1]
Question 39
The table gives measurements for waves produced in the same stretched string when the driving frequency is changed.
| Driving frequency / Hz | Measured wavelength / m |
|---|---|
| 12.0 | 2.00 |
| 16.0 | 1.50 |
| 20.0 | — |
| 24.0 | 1.00 |
| 30.0 | 0.80 |
Complete the missing value of wavelength for one row.
[1]
Determine the wave speed for each row using the data.
[1]
State the relationship between frequency and wavelength for this string.
[1]
Explain why the wave speed is approximately constant.
[1]
Question 40
A smartphone app records the arrival of two sharp sounds made at known positions along a track. The table gives the separation of the sound source and phone and the recorded travel time.
| Trial | Distance / m | Travel time / s |
|---|---|---|
| 1 | 20.0 | 0.058 |
| 2 | 30.0 | 0.088 |
| 3 | 40.0 | 0.117 |
| 4 | 50.0 | 0.129 |
| 5 | 60.0 | 0.176 |
| 6 | 70.0 | 0.205 |
Use one trial to calculate the speed of sound.
[1]
Use all the data to estimate a best value for the speed of sound.
[1]
Identify one anomalous result, if present.
[1]
Suggest one improvement to reduce percentage uncertainty in the timing.
[1]
Question 41
Light of different colours travels from air into a transparent material. The table gives the frequency of each light and its speed in the material.
| Colour | Frequency / Hz | Speed / m s⁻¹ |
|---|---|---|
| Red | 4.30 × 10¹⁴ | 2.04 × 10⁸ |
| Yellow | 5.20 × 10¹⁴ | 2.02 × 10⁸ |
| Green | 5.60 × 10¹⁴ | 2.01 × 10⁸ |
| Blue | 6.40 × 10¹⁴ | 1.99 × 10⁸ |
| Violet | 7.20 × 10¹⁴ | 1.97 × 10⁸ |
Calculate the wavelength in the material for one colour.
[1]
Compare the wavelength of this colour in the material with its wavelength in air.
[1]
Explain why the frequency is unchanged at the boundary.
[1]
Suggest why different colours may leave a prism in different directions.
[1]
Question 42
A mechanical wave travels along a stretched spring.
Describe the difference between transverse and longitudinal travelling waves.
[1]
Explain, using the wave model, how a travelling wave can transfer energy along the spring without net transfer of the spring material.
[1]
Question 43
A school laboratory uses two different methods to measure the speed of sound in air: an echo method and a two-microphone oscilloscope method.
Outline the echo method for determining the speed of sound.
[1]
Discuss the advantages of the two-microphone method compared with the echo method.
[1]
Question 44
Electromagnetic waves and sound waves can both transfer energy and information.
State two similarities between electromagnetic waves and sound waves.
[1]
Compare and contrast electromagnetic waves and sound waves in terms of their nature, propagation and examples of use.
[1]
Question 45
A detector measures electromagnetic radiation from a small source. The graph shows intensity against 1/r², where r is the distance from the source.
State what feature of the graph would support an inverse square relationship.
[1]
Use the graph to determine the emitted power of the source.
[1]
Identify one reason for a non-zero intercept, if present.
[1]
Explain why the model may fail very close to the source.
[1]
Question 46
A student models a small lamp as a point source of electromagnetic radiation.
Derive the inverse square relationship for intensity at distance r from a source of power P.
[1]
Evaluate the usefulness and limitations of this model for predicting the intensity measured by a light sensor in a classroom.
[1]
Question 47
A sinusoidal wave travels to the right along a string. A displacement–distance graph is available for one instant.
Explain how the graph can be used to identify wavelength and amplitude.
[1]
Explain how to determine the instantaneous direction of motion of different points on the string from the graph and the known direction of wave travel.
[1]
Question 48
A longitudinal sound wave travels through air from a loudspeaker to a microphone.
Describe the motion of air molecules and the pressure variation in the wave.
[1]
Discuss why particle displacement and pressure variation are not maximum at the same position, and how this affects interpretation of displacement–distance graphs for sound.
[1]
Question 49
A beam of white light passes from air into glass and then emerges from a prism as a spread of colours.
Explain what happens to the frequency, speed and wavelength of a single colour of light as it enters glass.
[1]
Evaluate how the wave model accounts for dispersion of white light by a prism, and state one limitation of using only this simple model.
[1]
Question 50
A deep-space probe communicates with Earth using radio waves. Engineers also consider using ultrasound for communication inside a liquid-filled tank on the probe.
Compare radio waves and ultrasound as travelling waves.
[1]
Evaluate why radio waves are suitable for communication across space whereas ultrasound is suitable only inside material media such as liquids or solids. Include discussion of energy spreading.
[1]
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