The diagram shows a wave travelling along a rope. The source is moved from side to side, and the rope itself moves up and down as the wave travels along its length. The distance from the midpoint (rest position) up to a crest is 0.4 m. The horizontal distance between two adjacent crests is 1.6 m.
(a)State the amplitude of the wave.(1)
(b)State the wavelength of the wave.(1)
(c)State whether this wave is transverse or longitudinal. Give a reason for your answer, based on the direction of the oscillations compared with the direction the wave travels.(2)
2
Sound waves travel through air as a series of compressions and rarefactions of air particles. Ripples on the surface of a pond make a floating leaf move up and down as the wave itself travels sideways across the pond.
(a)State whether sound waves are transverse or longitudinal.(1)
(b)State whether the ripples on the pond are transverse or longitudinal.(1)
(c)Give one similarity and one difference between transverse and longitudinal waves.(2)
3
A water wave in a ripple tank has a frequency of 5 Hz and a wavelength of 0.3 m. Use the wave equation: wave speed (m/s) = frequency (Hz) x wavelength (m).
(a)Calculate the speed of this wave.(2)
(b)A different wave has a speed of 10 m/s and a wavelength of 2 m. Rearrange the wave equation and calculate the frequency of this wave.(3)
4
Priya stands 170 m from a tall cliff and shouts. Assume the speed of sound in air is 340 m/s.
(a)Calculate the time taken for Priya to hear the echo of her shout, from the moment she shouts.(3)
(b)Priya then calculates the distance to the cliff as: distance = speed x time = 340 x 1.0 = 340 m. Explain the mistake in Priya's calculation and state the correct distance to the cliff.(2)
5
Required Practical: A student investigates the speed of sound in air. The student stands 200 m from a large flat wall, fires a starting pistol, and starts a stopwatch on seeing the flash of the pistol. The student stops the stopwatch on hearing the echo. This is repeated three times. Results: Trial 1: 1.18 s Trial 2: 1.24 s Trial 3: 1.16 s
(a)Suggest why the student starts the stopwatch on seeing the flash rather than on hearing the bang of the pistol.(1)
(b)Calculate the mean time taken for the sound to travel to the wall and back.(2)
(c)Calculate the speed of sound in air using the mean time from part (b). Use speed = distance / time.(3)
(d)Give one reason why repeating the experiment and calculating a mean improves the reliability of the result.(1)
(e)Suggest one improvement to the method that would make the measured speed of sound more accurate.(2)
6
Astronauts on the Moon cannot hear each other speak directly through the air; they must use radios to communicate.
(a)Explain why sound cannot travel through the vacuum of space.(2)
(b)State whether radio waves can travel through a vacuum.(1)
7
A red T-shirt is viewed in white light.
(a)Explain why the T-shirt appears red in white light.(2)
(b)The same T-shirt is now viewed under a blue filtered light, so that only blue light reaches the T-shirt. Predict and explain what colour the T-shirt will appear.(3)
8
A ray of light hits a plane (flat) mirror. The angle between the incident ray and the surface of the mirror is 35 degrees.
(a)Calculate the angle of incidence, measured from the normal.(2)
(b)State the size of the angle of reflection.(1)
(c)State the law of reflection.(1)
9
A ray of light travels from air into a glass block and bends towards the normal.
(a)Name the effect that causes the light ray to change direction as it enters the glass.(1)
(b)Explain, in terms of the speed of light, why the ray bends towards the normal as it enters the glass.(2)
(c)The ray then exits the glass block through a face parallel to the one it entered. State the direction of the emergent ray, compared with the original incident ray.(1)
10
For each statement about pitch and loudness, identify the correct option.
(a)Increasing the amplitude of a sound wave makes the sound:(1)
A) Louder
B) Higher pitched
(b)Increasing the frequency of a sound wave makes the sound:(1)
A) Louder
B) Higher pitched
(c)A bass guitar string, compared with a violin string, usually produces a sound with a:(1)
A) Lower frequency
B) Higher frequency
(d)A quieter sound of the same pitch would show, on an oscilloscope trace:(1)
A) A smaller amplitude trace
B) A larger amplitude trace
11
The normal human hearing range is approximately 20 Hz to 20,000 Hz. A dog whistle emits sound at a frequency of 35,000 Hz.
(a)State whether a human can hear the dog whistle directly. Give a reason for your answer.(2)
(b)Sound waves with a frequency above the upper limit of human hearing are given a specific name. State this name.(1)
(c)Give one medical use of ultrasound.(1)
12
A sound wave has a frequency of 250 Hz. Use the equation: time period T (s) = 1 / frequency f (Hz).
(a)Calculate the time period of this wave. Give your answer in standard form.(3)
13
Priya sees a flash of lightning. She counts 6 seconds before she hears the thunder. Assume the speed of sound in air is 340 m/s, and that the time for the light to reach Priya is negligible.
(a)Calculate the distance between Priya and the lightning strike.(3)
(b)Give your answer to part (a) in kilometres.(1)
14
Compare how light waves and sound waves transfer energy, and explain one key difference in how each type of wave behaves. In your answer, refer to: whether each wave is transverse or longitudinal; what each wave needs in order to travel; and one everyday application of each wave type.
(6)
15
Required Practical: A student investigates refraction by directing a ray of light from a ray box into a rectangular glass block, and measuring the angle of incidence and the angle of refraction with a protractor. Results: angle of incidence = 40 degrees, angle of refraction = 25 degrees.
(a)Name the piece of equipment used to measure the angles in this experiment.(1)
(b)State which angle is larger, the angle of incidence or the angle of refraction, and explain what this shows about the change in the speed of light as it enters the glass.(2)
(c)The student repeats the experiment using a Perspex block instead of a glass block, to compare the two materials. State one variable that must be kept the same for this to be a fair comparison.(1)
(d)Suggest one reason the point where the ray enters the block might be difficult to mark accurately, and suggest how the student could improve this.(2)
16
A simple periscope uses two plane mirrors, each angled at 45 degrees to the horizontal, to allow a viewer to see over an obstacle.
(a)A ray of light enters the periscope horizontally and strikes the first mirror. State the angle of incidence at this mirror, measured from the normal.(1)
(b)Explain why two mirrors are used in a periscope, rather than just one.(2)
17
An oscilloscope trace of a sound wave shows 4 complete waves in 0.02 s.
(a)Calculate the frequency of this sound wave.(3)
18
Visible light travels at a speed of 3 x 108 m/s. A red light wave has a frequency of 4.3 x 1014 Hz. Use the wave equation to calculate the wavelength of this light wave.
(a)Calculate the wavelength of this light wave. Give your answer in standard form.(3)
19
Choose the correct answer for each statement about waves.
(a)Which type of wave is a sound wave?(1)
A) Transverse
B) Longitudinal
C) Electromagnetic
D) None of these
(b)Which of these can travel through a vacuum?(1)
A) Sound
B) Light
C) Both
D) Neither
(c)The unit of frequency is:(1)
A) Metres
B) Seconds
C) Hertz
D) Newtons
(d)The distance between two adjacent crests of a wave is called the:(1)
A) Amplitude
B) Frequency
C) Wavelength
D) Period
(e)Doubling the frequency of a wave, while keeping the wave speed constant, will:(1)
A) Double the wavelength
B) Halve the wavelength
C) Have no effect on the wavelength
D) Double the wave speed
20
A shout produces an echo when it reflects off a distant wall.
(a)State what is meant by the term 'echo'.(1)
(b)Explain why an echo is not usually heard when shouting inside a small, carpeted room.(2)
Mark scheme · K14 Waves: Light and Sound
Question 1
(a) B1 0.4 m, cao
(a) Answer: 0.4 m
(b) B1 1.6 m, cao
(b) Answer: 1.6 m
(c) B1 transverse
(c) B1 reason: the rope oscillates up and down at right angles (perpendicular) to the direction the wave travels along the rope, oe
(c) Answer: Transverse; the rope's oscillations are perpendicular to the direction of energy transfer.
Question 2
(a) B1 longitudinal, cao
(a) Answer: Longitudinal
(b) B1 transverse, cao
(b) Answer: Transverse
(c) B1 similarity: both transfer energy from one place to another without an overall (net) transfer of matter/the medium, oe
(c) B1 difference: in transverse waves the oscillations are at right angles to the direction of energy transfer, but in longitudinal waves the oscillations are parallel to (along) the direction of energy transfer, oe
(c) Answer: Similarity: both transfer energy without net movement of matter. Difference: oscillation direction relative to travel direction (perpendicular vs parallel).
Question 3
(a) M1 correct substitution: wave speed = 5 x 0.3
(a) A1 1.5 m/s, cao
(a) Answer: 1.5 m/s
(b) M1 correct rearrangement: frequency = wave speed / wavelength
(b) A1 correct substitution: 10 / 2
(b) A1 5 Hz, cao
(b) Answer: 5 Hz
Question 4
(a) M1 total distance travelled by the sound = 2 x 170 = 340 m
(b) B1 Priya has not accounted for the sound travelling to the cliff AND back; 340 m is the total (there-and-back) distance, not the one-way distance, oe
(b) B1 correct distance = 170 m, ft from candidate's own value in (a) if the same error method is shown
(b) Answer: Mistake: 340 m is the round-trip distance, not the one-way distance. Correct distance = 170 m.
Question 5
(a) B1 light travels so much faster than sound that the flash is seen effectively at the same instant the pistol fires, so it gives a much more precise starting point for the timing than reacting to a second sound, oe
(a) Answer: Because light reaches the student almost instantly, giving a far more precise start time than waiting to hear a bang.
(b) M1 (1.18 + 1.24 + 1.16) / 3
(b) A1 1.19 s, awrt
(b) Answer: 1.19 s (awrt)
(c) M1 total distance travelled by sound = 2 x 200 = 400 m
(c) A1 335 m/s, awrt, ft from candidate's mean time in (b)
(c) Answer: 335 m/s (awrt)
(d) B1 it reduces the effect of random errors, such as the student's reaction time varying between trials, on the final calculated value, oe
(d) Answer: It reduces the effect of random errors (e.g. varying reaction time) on the final result.
(e) B1 e.g. use an electronic timer/data logger triggered automatically by a microphone at the start and the returning echo, instead of relying on human reaction time, oe
(e) B1 explanation: this removes human reaction time delays from both the start and the stop of the timing, oe (accept alternative valid improvement with matching explanation, e.g. increase the distance to the wall so that the fixed reaction-time error becomes a smaller proportion of the total time measured)
(e) Answer: Use an automatic electronic timer/data logger triggered by sound, removing human reaction-time errors from the timing.
Question 6
(a) B1 sound is caused by vibrations of particles, and needs a medium (solid, liquid or gas) of particles to travel through, oe
(a) B1 a vacuum contains no particles, so there is nothing to vibrate/carry the compressions and rarefactions of the sound wave, oe
(a) Answer: Sound needs particles to vibrate; a vacuum has no particles, so sound cannot travel through it.
(b) B1 yes, radio waves are electromagnetic waves and do not need particles/a medium to travel, oe
(b) Answer: Yes, radio waves can travel through a vacuum.
Question 7
(a) B1 the dye in the T-shirt reflects red light and absorbs the other colours (wavelengths) present in the white light, oe
(a) B1 only the reflected red light enters the eye, so the T-shirt appears red, oe
(a) Answer: The T-shirt reflects only red light and absorbs the rest, so only red light reaches the eye.
(b) B1 the T-shirt will appear black, oe
(b) B1 the dye absorbs blue light rather than reflecting it (it only reflects red light), oe
(b) B1 since no red light is available to reflect, and the blue light is absorbed, no light is reflected into the eye, oe
(b) Answer: Black; the dye absorbs the blue light and has no red light available to reflect, so no light reaches the eye.
Question 8
(a) M1 90 - 35
(a) A1 55 degrees, cao
(a) Answer: 55 degrees
(b) B1 55 degrees, ft from candidate's answer to (a)
(b) Answer: 55 degrees
(c) B1 the angle of incidence is equal to the angle of reflection, both measured from the normal, oe
(c) Answer: The angle of incidence equals the angle of reflection (measured from the normal).
Question 9
(a) B1 refraction
(a) Answer: Refraction
(b) B1 light travels more slowly in glass than in air, because glass is a (more optically) denser medium, oe
(b) B1 when a wave slows down on entering a denser medium at an angle (not along the normal), it changes direction and bends towards the normal, oe
(b) Answer: Light slows down entering the denser glass, causing the ray to bend towards the normal.
(c) B1 the emergent ray travels parallel to the original incident ray (it is sideways-displaced), oe
(c) Answer: Parallel to the original incident ray, but shifted sideways.
Question 10
(a) B1 A
(a) Answer: A) Louder
(b) B1 B
(b) Answer: B) Higher pitched
(c) B1 A
(c) Answer: A) Lower frequency
(d) B1 A
(d) Answer: A) A smaller amplitude trace
Question 11
(a) B1 no
(a) B1 35,000 Hz is above the upper limit of human hearing (20,000 Hz), oe
(a) Answer: No, because 35,000 Hz is above the upper limit of human hearing (20,000 Hz).
(b) B1 ultrasound
(b) Answer: Ultrasound
(c) B1 e.g. prenatal (pregnancy) scanning to image a foetus, or breaking up kidney stones, oe (accept any valid medical use)
(c) Answer: Prenatal scanning to produce images of a foetus (or breaking up kidney stones).
Question 12
(a) M1 correct substitution: T = 1 / 250
(a) A1 0.004 s
(a) A1 4 x 10-3 s, cao (standard form)
(a) Answer: 4 x 10-3 s (0.004 s)
Question 13
(a) M1 correct method: distance = speed x time
(a) M1 correct substitution: 340 x 6
(a) A1 2040 m, cao
(a) Answer: 2040 m
(b) B1 2.04 km, ft from candidate's answer to (a)
(b) Answer: 2.04 km
Question 14
Level 1 (1-2): Basic, largely isolated statements are made about light and/or sound, with limited or no accurate comparison. Little or no reference to wave type, medium, or applications.
Level 2 (3-4): Some accurate comparison points are made, with partial explanation linking wave type (transverse/longitudinal) and/or medium requirements to light and sound. At least one relevant application is given. The answer has some structure.
Level 3 (5-6): A detailed, logically structured comparison is given, correctly covering wave type, medium requirements, and applications for both light and sound, with clear and accurate scientific reasoning linking the ideas throughout.
Indicative content:
Light is a transverse wave; sound is a longitudinal wave.
In a transverse wave the oscillations are perpendicular (at right angles) to the direction of energy transfer; in a longitudinal wave the oscillations are parallel to (along) the direction of energy transfer.
Light is an electromagnetic wave and does not need a medium/particles to travel, so it can travel through a vacuum.
Sound needs a medium containing particles (solid, liquid or gas) because it travels as compressions and rarefactions of particles.
Both light and sound waves transfer energy without an overall (net) transfer of matter.
Light travels much faster than sound (about 3 x 10^8 m/s compared with about 340 m/s for sound in air), which is why thunder is heard after lightning is seen.
Both light and sound can be reflected (e.g. echoes for sound, mirrors for light) and can be refracted.
Example use of light: e.g. optical fibres for communication, mirrors/periscopes, or photography.
Example use of sound: e.g. ultrasound for medical scanning, sonar for detecting underwater objects, or musical instruments.
Question 15
(a) B1 protractor
(a) Answer: Protractor
(b) B1 the angle of incidence (40 degrees) is larger than the angle of refraction (25 degrees)
(b) B1 this shows the light slows down as it enters the (more optically dense) glass block, causing it to bend towards the normal, oe
(b) Answer: Angle of incidence (40 degrees) is larger; this shows light slows down entering the denser glass.
(c) B1 e.g. the angle of incidence, the position/brightness of the ray box, or the thickness/shape of the block, oe (accept any one valid controlled variable)
(c) Answer: The angle of incidence (or ray box position, or block thickness) must be kept the same.
(d) B1 reason: a wide beam of light makes the exact entry point on the outline of the block hard to identify precisely, oe
(d) B1 improvement: e.g. use a narrower ray/single slit, or mark the path of the ray with a series of dots before drawing a straight line through them, oe
(d) Answer: A wide beam makes the entry point unclear; using a narrower ray or marking dots along the ray path improves accuracy.
Question 16
(a) B1 45 degrees
(a) Answer: 45 degrees
(b) B1 the first mirror redirects the light downward/sideways, but the viewer needs to look in the same horizontal direction as they started, oe
(b) B1 the second mirror redirects the light back to travel horizontally, so it enters the viewer's eye in the original viewing direction, oe
(b) Answer: One mirror alone would send the light off at an angle; a second mirror redirects it back to horizontal so the viewer looks straight ahead.
Question 17
(a) M1 time period T = 0.02 / 4
(a) dM1 frequency f = 1 / T (using candidate's value of T)
(a) A1 200 Hz, cao
(a) Answer: 200 Hz
Question 18
(a) M1 correct rearrangement: wavelength = speed / frequency
(a) M1 correct substitution: (3 x 108) / (4.3 x 1014)
(a) A1 6.98 x 10-7 m, awrt (accept awrt 7.0 x 10-7 m)
(a) Answer: 6.98 x 10-7 m (awrt 7.0 x 10-7 m)
Question 19
(a) B1 B
(a) Answer: B) Longitudinal
(b) B1 B
(b) Answer: B) Light
(c) B1 C
(c) Answer: C) Hertz
(d) B1 C
(d) Answer: C) Wavelength
(e) B1 B
(e) Answer: B) Halve the wavelength
Question 20
(a) B1 the reflection of a sound wave off a hard, flat surface, oe
(a) Answer: A reflection of a sound wave off a hard surface.
(b) B1 in a small room, any reflected sound arrives back too soon after the original sound for the ear/brain to distinguish them as two separate sounds, oe
(b) B1 soft materials such as carpet absorb sound rather than reflecting it strongly, so less sound is reflected back anyway, oe
(b) Answer: The reflected sound returns too quickly to be heard separately, and soft surfaces like carpet absorb sound rather than reflecting it.