HKDSE · DSE Physics
DSE Physics: Wave Motion — Practice Questions & Answers
The nature and properties of waves, reflection, refraction and lenses, diffraction and interference, light and the EM spectrum, and sound.
396 practice questions available for this topic — here are 10 with full answers and explanations.
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Practice questions with answers
1
Multiple choice · Easy
A transverse pulse on a string is reflected at a fixed end. The reflected pulse
- is inverted and travels in the opposite direction
- keeps the same orientation and direction
- keeps the same orientation but reverses direction
- is inverted but keeps the same direction
Tap an answer to check it.
WhyReflection at a fixed end inverts the pulse and reverses its direction of travel.
2
Multiple choice · Medium
A pulse reflected at a fixed end undergoes a phase change of pi, but a pulse reflected at a free end undergoes a phase change of
Tap an answer to check it.
WhyA free end reflects with no phase change (zero); a fixed end gives a pi phase change.
3
Multiple choice · Hard
On reflection at a fixed end, which set of wave properties is unchanged?
- speed, frequency and wavelength
- direction of travel and phase
- frequency and direction only
- amplitude and direction only
Tap an answer to check it.
WhyReflection preserves speed, frequency and wavelength; only direction reverses and (at a fixed end) the phase inverts.
4
Fill in the blank · Easy
A pulse reflected from a fixed end of a string is (turned upside down).
Answer:
inverted
WhyFixed-end reflection inverts the pulse.
5
Fill in the blank · Medium
Reflection at a free end produces a phase change of .
Answer:
zero / 0
WhyA free end gives zero phase change.
6
Fill in the blank · Hard
When a wave reflects, its frequency and wavelength are unchanged, so its wave is also unchanged.
Answer:
speed
WhySince v = f x wavelength and both are unchanged, the wave speed is unchanged.
7
Multiple choice · Easy
In a vacuum, radio waves, visible light and X-rays all travel at
- the same speed
- speeds that increase with frequency
- speeds that decrease with frequency
- the speed of sound
Tap an answer to check it.
WhyAll electromagnetic waves have the same speed c in a vacuum.
8
Multiple choice · Medium
Which of the following statements is INCORRECT?
- In air, the wavelength of infra-red radiation is shorter than that of ultra-violet radiation
- Visible light travels faster in air than in glass
- Microwaves travel at the speed of light in a vacuum
- Both light and sound can exhibit diffraction
Tap an answer to check it.
WhyInfra-red has a longer wavelength than ultra-violet, so stating it is shorter is incorrect.
9
Multiple choice · Hard
When light travels from air into glass, which quantity stays the same?
- its frequency
- its speed
- its wavelength
- its direction
Tap an answer to check it.
WhyFrequency is set by the source and does not change; speed and wavelength both decrease in glass.
10
Fill in the blank · Easy
Ordered by increasing frequency, infra-red comes ultra-violet.
Answer:
before
WhyIR has a lower frequency, so it comes before UV.
Key terms in Wave Motion
Wave: A disturbance that transfers energy from one place to another without transferring matter.
Transverse wave: A wave in which the vibration is perpendicular to the direction of energy travel, such as light.
Longitudinal wave: A wave in which the vibration is parallel to the direction of energy travel, such as sound.
Wavelength: The distance between two successive points in phase on a wave, such as crest to crest.
Frequency: The number of complete waves passing a point each second, measured in hertz.
Amplitude: The maximum displacement of a particle from its rest position as a wave passes.
Period: The time taken for one complete wave or oscillation, equal to one divided by the frequency.
Wave speed: The speed at which a wave travels, given by v = f lambda where lambda is the wavelength.
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