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Read the passage, then answer the questions.
A wave transfers energy from one place to another without transferring matter.
Waves are caused by something vibrating (oscillating).
When a wave travels through a material, the particles vibrate about a fixed point but do not travel with the wave.
Read the passage, then answer the questions.
In a transverse wave, the vibrations are at right angles (perpendicular) to the direction of energy transfer. Example: water waves and all EM waves.
In a longitudinal wave, the vibrations are parallel to the direction of energy transfer. Example: sound waves.
In a longitudinal wave, regions where particles are close together are compressions; regions where they are spread out are rarefactions.
Read the passage, then answer the questions.
Both types transfer energy and have the same wave properties (wavelength, frequency, amplitude).
The key difference is the direction of vibration relative to the wave’s travel.
You need to be able to recall examples of each type of wave for AQA GCSE Physics:
| Transverse waves | Longitudinal waves |
|---|---|
| ▸ All electromagnetic waves: radio, microwave, infrared, visible light, ultraviolet, X-ray, gamma ray ▸ Ripples/waves on the surface of water ▸ S-waves (secondary seismic waves) ▸ A rope or slinky spring shaken side to side | ▸ Sound waves (in air, liquids and solids), including ultrasound ▸ P-waves (primary seismic waves) ▸ A slinky spring pushed and pulled along its length, producing compressions and rarefactions |
Read the passage, then answer the questions.
Amplitude is the maximum displacement of a point on a wave away from its undisturbed position.
Wavelength (λ) is the distance from a point on one wave to the equivalent point on the adjacent wave (e.g. crest to crest). It is measured in metres (m).
For a sound wave, a bigger amplitude means a louder sound.
Read the passage, then answer the questions.
Frequency (f) is the number of waves passing a point each second, measured in hertz (Hz).
The period (T) is the time taken for one complete wave to pass a point, measured in seconds (s).
For a sound wave, a higher frequency means a higher pitch.
Period and frequency are linked by the AQA equation:
A wave has a frequency of 50 Hz. Find its period.
A wave has a period of 0.2 s. Find its frequency.
Read the passage, then answer the questions.
You can find a wave’s properties directly from a graph: wavelength and amplitude from a displacement–distance graph; period from a displacement–time graph (then use T = 1/f to find frequency).
Worked Example: Finding Wavelength from a Graph
Worked Example: Finding Amplitude from a Graph
Use Fig 2.4 to find the frequency of the wave.
Read the passage, then answer the questions.
Wave speed is the speed at which the energy is transferred (or the wave moves) through the medium.
The speed of a wave is linked to its frequency and wavelength by the AQA equation:
where v is wave speed in m/s, f is frequency in Hz and λ is wavelength in m.
A wave has frequency 12 Hz and wavelength 3 m. Find its speed.
Read the passage, then answer the questions.
If you know v and need to find f or λ, substitute the numbers into the given equation v = fλ first, then rearrange to solve; see the worked examples in Part 1.
Always check the units match (speed in m/s needs wavelength in m and frequency in Hz).
A 170 Hz sound wave travels at 340 m/s. Find λ.
A wave travels at 20 m/s with a wavelength of 4 m. Find f.
Read the passage, then answer the questions.
Required practical: measure the speed of waves in a ripple tank and waves in a solid (e.g. a stretched string).
Ripple tank: measure the wavelength by photographing the waves against a ruler. Measure ten wavelengths and divide by ten for accuracy.
Measure the frequency by counting the waves passing a point in 10 s and dividing by 10. Then use v = fλ.
Method: Ripple Tank
Stretched string: attach a string to a vibration generator, with the other end passing over a pulley with a weight to keep it taut.
Turn on the generator and adjust its frequency until a clear standing wave pattern (with fixed nodes) forms along the string.
Method: Stretched String
Speed of sound in air: two students stand a measured distance apart, at least 100 m, on an open field. One bangs two blocks of wood together; the other starts a stopwatch when they see the blocks hit and stops it when they hear the sound.
Speed = distance ÷ time. Repeat several times and take a mean, because the reaction time of the person with the stopwatch is a large source of random error.
Method: Speed of Sound in Air
Read the passage, then answer the questions.
When a wave hits a surface it can be reflected. We measure angles from the normal (a line at 90° to the surface).
The law of reflection: the angle of incidence equals the angle of reflection.
Read the passage, then answer the questions.
When a wave passes into a different material it can change speed and direction: this is refraction.
Light slows down when it enters a denser material (e.g. air → glass), so it bends towards the normal.
When light speeds up (glass → air) it bends away from the normal.
Read the passage, then answer the questions.
When a wave reaches a boundary between two materials, three things can happen: it can be reflected (bounces back), transmitted (passes through, possibly refracted) or absorbed (its energy is transferred to the material).
Usually a mixture happens: for example, light hitting a window is mostly transmitted, partly reflected (you can see a faint reflection) and slightly absorbed.
The law of reflection applies to all types of wave, not just light.
Refraction happens at a boundary only if the wave changes speed; the bigger the speed change, the more it bends.
| Angle of incidence | Angle of reflection | |||
|---|---|---|---|---|
| Test 1 | Test 2 | Test 3 | Test 4 | |
| 20° | 19° | 22° | 20° | 19° |
| 30° | 31° | 28° | 32° | 30° |
| 40° | 42° | 40° | 43° | 41° |
| 50° | 56° | 49° | 53° | 46° |
| Angle of incidence | Angle of refraction |
|---|---|
| 20° | 13° |
| 30° | 19° |
| 40° | 25° |
| 50° | 30° |
Read the passage, then answer the questions.
The electromagnetic (EM) spectrum is a family of 7 types of wave.
All EM waves are transverse and travel at the same speed (the speed of light, 3.0 × 10⁸ m/s) in a vacuum.
In order of increasing frequency (and energy): radio, microwave, infrared, visible, ultraviolet, X-ray, gamma.
EM waves are generated or absorbed when changes happen inside atoms or their nuclei. Gamma rays come from changes in the nucleus.
Read the passage, then answer the questions.
Across the spectrum, as wavelength decreases, frequency increases and so does energy.
X-rays and gamma rays are ionising radiation and can be harmful. UV is also harmful (it can damage skin and eyes) even though it carries less energy than X-rays or gamma rays.
Read the passage, then answer the questions.
Like all waves, EM waves can be refracted when they pass into a different material, changing speed and direction.
Different materials change the speed by different amounts, which is why a prism can separate white light into colours.
(HT only) Explaining refraction with wave fronts: when a wave front meets the boundary at an angle, the part that enters the glass first slows down while the rest is still travelling faster in the air. This swings the wave front round, so the wave changes direction towards the normal. The frequency does not change, so the slower wave has a shorter wavelength: the wave fronts are closer together in the glass (Fig 5.2).
| Electromagnetic wave | Use |
|---|---|
| Gamma rays | |
| Microwaves | |
| Ultraviolet |
Read the passage, then answer the questions.
Each EM wave is used for jobs that suit its properties:
Radio: TV and radio broadcasts (long wavelength, so they diffract around hills and buildings and travel long distances).
Microwaves: mobile phones, satellite communications and microwave ovens.
Infrared: electrical heaters, cooking food, infrared (thermal imaging) cameras and remote controls.
Visible light: seeing and fibre optic communications. UV: energy-efficient lamps and sun tanning. X-rays: medical images of bones. Gamma: sterilising equipment and treating cancer.
Read the passage, then answer the questions.
X-rays and gamma rays are ionising radiation: they can cause cell mutation and cancer.
Ultraviolet is also harmful: it can cause sunburn and skin cancer and damage eyes.
In general, the higher the frequency (and energy) of an EM wave, the more harmful it can be.
The harm done by UV, X-rays and gamma rays depends on the type of radiation and the size of the dose.
Radiation dose, measured in sieverts (Sv), is a measure of the risk of harm from exposure to radiation. 1000 millisieverts (mSv) = 1 sievert (Sv). You do not need to recall the unit, but you may be asked to compare doses from given data.
Read the passage, then answer the questions.
Radio waves can be produced by oscillations (alternating current) in an electrical circuit / aerial.
When radio waves are absorbed by an aerial, they create an alternating current with the same frequency, which carries the signal.
Read the passage, then answer the questions.
Infrared (IR) radiation transfers energy; all objects, whatever their temperature, emit and absorb infrared.
Matt black surfaces are the best absorbers and emitters of infrared.
Shiny, light-coloured surfaces are the worst absorbers and emitters (they reflect IR).
Read the passage, then answer the questions.
A perfect black body absorbs all radiation that hits it (reflecting and transmitting none) and is the best possible emitter.
All bodies emit a range of wavelengths. As an object gets hotter, it emits more radiation and the peak shifts to shorter wavelengths.
Read the passage, then answer the questions.
The temperature of an object depends on the balance between the radiation it absorbs and the radiation it emits.
If an object absorbs more than it emits, its temperature rises; if it emits more than it absorbs, it cools.
Read the passage, then answer the questions.
This required practical investigates how the nature of a surface affects the amount of infrared radiation it emits.
A Leslie cube is a hollow metal cube with four different outer faces: matt black, shiny black, matt white and shiny silver. It is filled with hot water so that all four faces are at the same temperature.
An infrared detector (or a thermometer with a blackened bulb) is held at a fixed distance from each face in turn and the reading is recorded.
Independent variable: the variable you change in an investigation.
Dependent variable: the variable you measure to see the effect of the change.
Control variables: the variables you keep the same so that the test is fair (valid).
Hypothesis: a prediction of what you expect to happen, with a scientific reason for it.
Safety: use water at or below 60 °C (hot water can scald), wear eye protection, do not overfill the cube, carry it on a heatproof mat and do not touch the metal faces.
Read the passage, then answer the questions.
Method: the distance between the detector and the face, and the time the detector is held there, must be the same for every face.
1. Place the Leslie cube on a heatproof mat and fill it with hot water from a kettle. Put the lid on.
2. Wait about one minute so that all four faces reach the same temperature.
3. Use a ruler to position the infrared detector 10 cm from the matt black face. Record the reading.
4. Repeat for the other three faces, keeping the distance and the time the same.
5. Repeat the whole set of readings twice more and calculate a mean for each face.
6. Record the results in a table and compare the readings for the four faces.
Taking repeat readings and calculating a mean makes the results more precise and makes it easier to spot an anomalous result, which should be left out when the mean is calculated.
If a thermometer with a blackened bulb is used instead of a detector, record the temperature rise of the thermometer after a fixed time (e.g. 2 minutes) at each face.
Results table: record your results during the practical below:
| Surface | Reading 1 | Reading 2 | Reading 3 | Mean |
|---|---|---|---|---|
| matt black | ||||
| shiny black | ||||
| matt white | ||||
| shiny silver |
Read the passage, then answer the questions.
The independent variable (the type of surface) is categoric, so the results are shown on a bar chart, not a line graph.
Typical results are shown in Fig 8.2: matt black gives the highest reading and shiny silver the lowest, with matt white and shiny black in between.
Conclusion: matt black surfaces are the best emitters of infrared and shiny, light-coloured surfaces are the worst emitters. Matt surfaces emit more than shiny ones, and dark surfaces emit more than light ones.
Evaluation: the cube cools during the experiment, so later readings are slightly lower than they should be. Take the readings quickly, repeat them in a different order, or top up the hot water.
| Surface | Detector reading (arbitrary units) |
|---|---|
| matt black | 20.5 |
| shiny black | 15.0 |
| matt white | 16.5 |
| shiny silver | 8.0 |
Read the passage, then answer the questions.
Sound is a longitudinal wave caused by vibrations; it needs a medium (it cannot travel through a vacuum).
Sound entering the ear makes the eardrum vibrate; these vibrations are passed on and converted into nerve signals.
The human hearing range is about 20 Hz to 20 000 Hz.
The eardrum, and other solids, can only be made to vibrate by sound over a limited range of frequencies. This is why human hearing is limited to roughly 20 Hz to 20 kHz.
Read the passage, then answer the questions.
An echo is a reflection of sound from a surface. If you know the speed of sound and time how long an echo takes to return, you can work out how far away the surface is. The sound travels there and back, so the distance is half of speed × time.
Bats use this to navigate in the dark: they emit high-frequency sound pulses and listen for the echoes from insects and obstacles. The time between pulse and echo tells the bat how far away an object is.
Echo sounding (sonar) uses the same idea at sea. A ship or submarine sends a pulse of high-frequency sound down through the water; the time for the echo to return from the seabed, a wreck or another vessel gives its distance. It is used to measure water depth and to detect objects in deep water.
A submarine’s sonar pulse returns from the seabed after 0.8 s. Sound travels at 1500 m/s in water. Find the depth.
Read the passage, then answer the questions.
Ultrasound is partly reflected at a boundary between two different materials.
By timing the returning echo, the distance to the boundary can be calculated. This is used in prenatal scans and to find flaws in metal.
Ultrasound is used for baby scans because it is non-ionising (safer than X-rays).
Read the passage, then answer the questions.
Earthquakes produce two types of seismic wave: P waves (longitudinal, travel through solids and liquids, but at different speeds in each) and S waves (transverse, travel through solids only).
P stands for primary and S for secondary: P waves travel faster, so they are the first to arrive at a seismometer after an earthquake, and S waves arrive second.
P waves are refracted at the core boundary because their speed changes, and S waves cannot pass through the liquid outer core. Together, these give evidence for the structure and size of the Earth’s core.
Read the passage, then answer the questions.
A convex (converging) lens bulges outwards (it is thicker in the middle than at the edges).
Rays of light parallel to the axis are brought together by a convex lens to a point called the principal focus, F. The distance from the centre of the lens to the principal focus is the focal length.
Lenses change the direction of light by refraction: the light bends as it enters and leaves the glass. A more curved (fatter) lens refracts the rays more, so it has a shorter focal length.
Read the passage, then answer the questions.
A real image is formed where the rays actually meet, so it can be projected onto a screen. On a ray diagram the refracted rays cross on the opposite side of the lens to the object. Examples: the picture on a cinema screen; the image on the sensor of a camera.
A virtual image is formed where the rays only appear to come from, so it cannot be projected onto a screen. On a ray diagram the refracted rays spread apart, so they are extended backwards with dashed lines and cross on the same side of the lens as the object. Examples: your reflection in a plane mirror; the enlarged image seen through a magnifying glass.
A magnified image is larger than the object (a magnifying glass, a projector). A diminished image is smaller than the object (a camera, the eye).
An upright image is the same way up as the object (a mirror, a magnifying glass). An inverted image is upside down (the image in a camera or on the back of the eye).
The image formed by a convex lens depends on where the object is (Fig 10.2):
How to draw a ray diagram for a convex lens
Read the passage, then answer the questions.
A concave (diverging) lens caves inwards (it is thinner in the middle than at the edges).
Rays of light parallel to the axis are made to spread out (diverge) by a concave lens. The refracted rays appear to come from a point on the same side as the incoming light: this is the principal focus, F, of the concave lens. Because the rays never actually pass through it, it is a virtual focus.
The focal length is the distance from the centre of the lens to F, just as for a convex lens.
Read the passage, then answer the questions.
A concave lens always produces a virtual, upright, diminished image, on the same side of the lens as the object, between the lens and F.
On the ray diagram the refracted rays spread apart and never meet, so the image is found where their dashed extensions cross; this is why the image is virtual and cannot be projected onto a screen.
How to draw a ray diagram for a concave lens
Read the passage, then answer the questions.
The magnification of a lens is found from the AQA equation:
Magnification has no units (it is a ratio). A value greater than 1 means the image is enlarged.
An object 2 cm tall forms an image 6 cm tall. Find the magnification.
Read the passage, then answer the questions.
White light is made of a spectrum of colours: red, orange, yellow, green, blue, indigo, violet.
Each colour of the visible spectrum has its own narrow band of wavelength and frequency.
A prism splits white light into these colours because each colour is refracted by a different amount.
Violet has the shortest wavelength and is refracted the most; red has the longest wavelength and is refracted the least.
Read the passage, then answer the questions.
A colour filter only lets through light of its own colour and absorbs the other colours.
A red filter transmits red light and absorbs the rest; a green filter transmits only green, and so on.
Read the passage, then answer the questions.
An opaque object’s colour is the colour of light it reflects; it absorbs the other colours.
A white object reflects all colours; a black object absorbs all colours.
If an object is lit by only one colour, it can look black if that colour is not one it reflects.
Reflection from a smooth surface in a single direction is called specular reflection (e.g. a mirror). Reflection from a rough surface causes scattering: this is called diffuse reflection (e.g. paper).
Objects that transmit light are either transparent (you can see clearly through them, e.g. glass) or translucent (light passes through but is scattered, so you cannot see clearly, e.g. frosted glass).
