AQA GCSE Single Science Physics: Waves

What is the difference between longitudinal and transverse waves? List examples of both

• Longitudinal waves have oscillations parallel to the direction of energy transfer (sound, ultrasound, seismic P-waves)

• Transverse waves have oscillations that are perpendicular to the direction of energy transfer (electromagnetic waves, ripples on water, seismic S-waves)

Define the following terms: amplitude, wavelength, frequency and period

• Amplitude: the maximum displacement of a point on a wave away from its undisturbed position.

• Wavelength: the distance from a point on one wave to the equivalent point on the adjacent wave.

• Frequency: the number of waves passing a point each second.

• Period: time it takes for one complete vibration

What is evidence for waves travelling and not the water or air itself (for ripples on a water surface or sound waves in air)?

• In water: place a small object (like a cork or a piece of paper) on the water's surface, it will bob up and down with the wave, but it won't move horizontally with the wave. 

• In air: when you push one end of a spring, the energy travels along the spring, but the spring coils themselves don't move with the energy. 

How would one calculate frequency and wave speed?

• Frequency = 1/(time) period

• Wave speed = frequency × wavelength

How would you measure waves in a solid?

1. Attach a string or cord to a vibration generator and use a hanging mass and pulley to pull the string taut. Place a wooden bridge under the string near the pulley.

2. Switch on the vibration generator and adjust the wooden bridge until stationary waves can be clearly observed.

3. Measure the length of as many half wavelengths (loops) as possible, divide by the number of half wavelengths (loops). This is half the wavelength, doubling this gives the wavelength.

4. The frequency is the frequency of the power supply.

5. Calculate the speed of the waves using: wave speed = frequency × wavelength.

How would you measure waves in a ripple tank?

1. Set up the ripple tank with about 5 cm depth of water.

2. Adjust the height of the wooden rod so that it just touches the surface of the water.

3. Switch on the lamp and motor and adjust until low frequency waves can be clearly observed.

4. Measure the length of a number of waves then divide by the number of waves to record wavelength. It may be more practical to take a photograph of the card with the ruler and take measurements from the still picture.

5. Count the number of waves passing a point in ten seconds then divide by ten to record frequency.

6. Calculate the speed of the waves using: wave speed = frequency × wavelength.

How would you measure the speed of sound waves in air? And what is a limitation of this method?

1. Have one person fire a pistol in the air a set distance away from a second person and raise their hand

2. Have the second person measure the duration of time between seeing the hand signal and hearing the sound of the gunshot

3. Use the formula: v = d/t to determine the speed of sound waves

However, this is a flawed experimental method as it is dependent on the second person’s reaction time.

What happens (in relation to wavelength, velocity and frequency) when a sound moves from a dense medium to a less dense medium?

• The wavelength of the sound wave decreases

• The frequency of the sound wave stays the same

• The velocity of the sound wave decreases

What may happen to a wave at a boundary between two mediums?

• Absorption

• Transmission

• Reflection

The object always has a proportion of all three responses but different types of waves react differently to different mediums.

How would you investigate reflection?

1. Place a mirror in the middle of a sheet of paper where a line has been drawn

2. Shine a ray of light from the ray box at the mirror and trace both the incident ray and the reflected ray, as well as measuring the angle of incidence and angle of reflection with a protractor

3. Repeat with different angles.

What are the control variables for the reflection practical?

• Distance of ray box from mirror

• Width of the light beam

• Same frequency / wavelength of the light

How would you investigate refraction?

1. Place a glass box in the middle of a sheet of paper- draw around this

2. Shine a ray of light from the ray box at the mirror and trace both the incident ray and the refracted ray, as well as measuring the angle of incidence and angle of refraction with a protractor and by finding the normals (lines perpendicular to the surface of the glass)

3. Repeat with different angles.

What are the control variables for the refraction practical?

• Use of the same perspex block

• Width of the light beam

• Same frequency / wavelength of the light

What happens when a sound wave hits a solid?

• Sound waves contain pressure variations due to compressions and rarefactions

• The surface of the solid vibrates in sync with the sound waves

Explain the process of sound being transmitted to the human ear

• The sound wave makes its way toward the eardrum through the auditory canal

• The pressure variations exert a varying force on the eardrum, causing it to vibrate in the same pattern of the sound wave

• This vibration is transferred to three small bones which transfer it to the inner ear where nerve cells transmit the information to the brain, making sound.

What is the range of frequencies a human can hear? Why?

• 20Hz - 20kHz

• The transmission of sound to the human ear only works over a limited range of frequencies due to the ear being small and delicate- any more would cause damage and any lower would not be detected.

• This limits the range of sound frequencies a human can hear

What are some examples of exploring structure using waves?

• Echo sounding; which measures the depth of water

• Ultrasound; which measures the time taken for the reflections to reach a detector and so can be used to determine how far away a boundary is.

• Seismic activity; which identifies whether a wave is an S-wave or P-wave by seeing whether it can be found in solids and liquids.

Which properties of a substance allow the detection of structures? How?

• Reflection

• Absorption

• Transmission

• The speed of sound in the substance

This is because

• Each type of substance will produce different amounts of reflection, absorption and transmission

• Each type of substance will also transmit a sound wave at a specific speed

What do seismic waves tell us about the structure of the Earth?

• S-waves can only be found in solids, while P-waves can travel through both solids and liquids.

• So as S-waves cannot be detected in the outer core but P-waves can, we can infer that the outer core is liquid.

What are EM waves? What are some of their properties?

• Electromagnetic waves are transverse waves that transfer energy from the source of the waves to an absorber.

• They form a continuous spectrum

• They all travel at the same velocity through a vacuum or air

• Substances may absorb, transmit, refract or reflect electromagnetic waves in ways that vary with wavelength

Plan an investigation on how the amount of infrared radiation absorbed/radiated by a surface depends on the surface

1. Place a Leslie cube on a heat-resistant mat. Fill it, almost to the top, with boiling water and replace the lid.

2. Leave for one minute. This is to enable the surfaces to heat up to the temperature of the water.

3. Use the infrared detector to measure the intensity of infrared radiation emitted from each surface, or the temperature of the surface. Make sure that the detector is the same distance from each surface for each reading.

How are radio waves produced? What happens when they are absorbed?

• They are produced by oscillations found in electrical circuits

• When absorbed, they can create an alternating current with the same frequency as the radio wave causing it

• This could then produce oscillations, forming more radio waves

What happens when the nucleus of an atom changes? Give an example

• Changes in atoms and the nuclei of atoms can result in electromagnetic waves being generated or absorbed over a wide frequency range.

• An example of this is the emission of gamma rays

What are the effects of specific EM waves? Name the hazardous ones and how their effects can be measured.

• UV radiation, gamma rays and X rays are hazardous to human health- the effects depend on the type of radiation and size of dose.

• UV rays can cause skin ageing and skin cancer

• X-rays and gamma rays increase the risk of cancer by increasing the risk of mutation and tissue ionisation

• Radiation dose (in sieverts) is a measure of the risk of harm resulting from an exposure of the body to the radiation.

What are the practical applications of EM waves? Why are they suitable for their function?

• Radio waves are used in television and radio; they are transmitted easily through air and can be reflected to change direction

• Microwaves are used in satellite communications and cooking food; they are easily absorbed by molecules in food and easily pass through the atmosphere

• Infrared is used in electrical heaters, cooking food and infrared cameras; when absorbed, increases internal energy of chemical bonds which causes heating effect

• Visible light is used in fibre optic communications; can be transmitted through glass

• Ultraviolet is used for energy efficient lamps and suntanning; helps to make vitamin D in the skin

• X-rays and gamma radiation is used for medical imaging and treatments; they are high frequency rays

What are the differences between a convex and concave lens?

• Convex lenses cause the light rays to converge (come together), are thicker in the middle, and have a principle focus after the lens. The image produced may either be virtual or real.

• Concave lenses cause the light rays to diverge (spread out), are thinner in the middle, and have a principle focus before the lens. The image produced is always virtual.

Define specular and diffuse reflection.

• Specular reflection is from a smooth surface in a single direction

• Diffuse reflection is from a rough surface and causes scattering

How do colour filters work?

• They absorb some wavelengths of light and transmit others

• The wavelengths they transmit are the colours that they appear

Explain the appearance of white, black and transparent objects

• An object appears white when it reflects each wavelength of light equally and absorbs none.

• An object appears black when it absorbs each wavelength of light equally and reflects none.

• An object appears transparent when it transmits the wavelengths of light and reflects and absorbs none.

What are some qualities of the perfect black body?

• Absorbs all radiation incident upon it

• Does not transmit or reflect any radiation

• Best possible emitter

How does temperature effect the radiation a body emits?

• At a constant temperature, radiation is balanced- amount of radiation that is absorbed is equal to the amount of radiation emitted

• If radiation is unbalanced, object temperature rises- amount of radiation that is absorbed is more than the amount emitted

• Increased temperature increases the intensity of the emission

• Increased temperature decreases the wavelength of the emission

Which factors does the temperature of the Earth depend on?

• Rates of emission and absorption- radiation is emitted by the Sun and absorbed by the Earth, increasing the temperature. Some of this radiation is absorbed by the atmosphere, lowering the temperature.

• Rates of reflection and radiation- the atmosphere reflects some solar radiation, decreasing the temperature and at night, the Earth emits radiation back into space, which also decreases the temperature.