| What are the two categories of waves? | The two categories of waves are transverse waves such as ripples on the surface of the water, and longitudinal waves such as sound waves traveling in air. |
| What do all waves do? | All waves transfer energy from one place to another, e.g. ripples transfer kinetic energy, and sound waves transfer sound energy. |
| What are oscillations? | Oscillations are the up and down movement of a wave. |
| At what angle are the oscillations in transverse waves? | In transverse waves, the oscillations are perpendicular (at right angles) to the direction of energy transfer.
So the oscillations are up and down while the direction of energy transfer is sideways/horizontal. |
| Why do sound waves travel? | Sound waves travel because particles in the air move from side to side. |
| What are compression and rarefactions in longitudinal waves? | In longitudinal waves, compressions are the regions where the air particles are very close together, while rarefactions are the regions where the air particles are spaced out. |
| What is the relationship between the oscillations and the direction of energy transfer in longitudinal waves? | In longitudinal waves, the oscillations are parallel to the direction of energy transfer. |
| What do all longitudinal waves require to travel? | All longitudinal waves require a medium to travel in e.g. air, a liquid, or a solid, but not all transverse waves require a medium. |
| how can a slinky be used to show waves are what travel on a water surface or in the air, and not the water or air? | A slinky can be used to prove waves travel on a water surface or in the air, not the water or air.
To do this place a red dot in a slinky. The red dot represents a water molecule. When the wave travels through the water the dot oscillate up and down, the dot does not travel along with the medium. The waves move not the water.
Similarly if the red dot represented an air particle, the dot would oscillate from side to side but not travel through the medium. |
| what is the amplitude of a wave? | The amplitude of a wave is the maximum displacement of a point on the wave away from its undistributed position, e.g. the distance from the undisturbed potion in the middle of the wave, to the crest and trough. |
| What is the wavelength in transverse and longitudinal waves? | In transverse waves, the wavelength is the distance from a point on one wave to the equivalent point on the adjacent wave e.g. the distance from two crests, troughs, or in the middle.
And in longitudinal waves the wavelength is from one compression or rarefaction to the next compression or rarefaction. |
| What is the frequency, period and period of a wave? | The frequency is the number of waves passing a point each second, measured in Hertz, while 1 Hz = 1 wave per second, so a wave with four waves would have a frequency of 4 Hz.
The period is the time in second for one wave to pass a point, which is calculated using the equation period (s) = 1/ frequency (Hz).
The wave speed is the speed at which the wave moves through the medium, i.e. the speed at which energy is transferred.And the wave speed equation is:
Wave speed (m/s) = frequency (Hz) x wavelength (m)
Where wavelength = ‘Lambda Greek symbol’ |
| How can the speed of a sound wave be calculated? | The speed of a sound wave can be calculated by diving the distance travelled by the time taken, for example, if person A was clashing cymbals, the distance between person A and person B would be divided by the time it took for the sound waves to reach person B. |
| What are the problems with calculating the speed of a sound wave by dividing the distance travelled by the time taken? | The problem with calculating the speed of a sound wave by dividing the distance travelled by the time taken, is every person has a different reaction time. This causes random errors but can be resolved a larger group making new measurements. These results would then be used to calculate a new mean.
Another problem is that the time between hearing the cymbals and seeing them clash is very short, making it difficult to press the timer at the right time. This may be solved by increasing the distance between person A and B, as a greater distance will give a greater waiting period to hear the cymbals clash. |
| What is a ripple tank sued to do? | A ripple tank is used to observe the wavelength, frequency, and speed of the water waves. |
| How do you set up a ripple tank to measure the wavelength of a wave, frequency and speed of a wave? | Firstly you need a ripple tank which is a shallow tray of water. The water has a vibrating bar inside, that is connected to a power pack.
The bar will vibrate, creating waves across the surface of the water.
Meanwhile, above the ripple tank should be a lamp and below it; a sheet of white paper. So when the light shines from the lamp through the light, an image of the waves will be produced on the paper.
This can be used to measure the wavelength, frequency, and speed of the water waves. |
| How is the wavelength of waves measured in the ripple tank practical? | In the ripple tank practical, to measure the wavelength of water waves, first, record the waves on a phone, so the recording can be played back at different speeds and paused.
Now measure the wavelength by placing a ruler on the paper. Pause the image of the waves, and measure the distance between the first and tenth wavelength.
Finding the wavelength of one wave is then calculated by dividing this distance by 10. |
| How is the frequency of waves measured? | To measure, the frequency of waves, place a timer next to the paper and count the number of waves passing a point in one second. Though it would be more accurate to count the number of waves in 10 seconds and divide that by 10. |
| How can you calculate the speed of waves? | The speed of waves can be calculated using the wave speed equation.
The speed of waves can be calculated by measuring the time it takes to move the total length of the tank.
And The speed of waves can be calculated by dividing the distance travelled by the time taken. |
| What is used to measure the features of waves in a solid? | To measure the features of waves in a solid attach a string to a vibration generator and attach a mass at the other end of the string. This keeps the string tense.
The vibration generator is attached to a single generator. This allows the frequency of vibration of the spring to be changed.
So when the power is turned on, the string vibrates. |
| What is a standing wave and how can it’s frequency be measured? | A standing wave is a wave that is visible to the human eye due to resonance, that are found in string musical instruments such as a violin.
And the frequency of a standing wave can be measured using a ruler to measure the length of the wave from the wooden bridge to the vibration generator. |
| What happens if the frequency of a standing wave is increased? | If the frequency of a standing wave is increased three half wavelengths are produced from two full wavelengths. |
| How can the wavelength of three half waves be calculated? | The wavelength of three half waves can be calculated by dividing the total length by the number of half-waves e.g. 24cm/ 3 half-waves and then multiplying by two |
| What is an electromagnetic wave? | An electromagnetic wave is a transverse wave, that transfers energy from the source of the waves to the absorber, e.g. a microwave, that transfers energy from the source of the waves; the oven, to the absorber; food, and solar panels that use light waves to transfer energy from the source; the Sun, to the absorber; solar panels on the spacecraft. |
| What is the electromagnetic spectrum? | The visible part of the electromagnetic spectrum is the spectrum of each colour of the light (passed through a prism) that have different wavelengths and frequencies. The order of the spectrum is red, orange, yellow, green, blue, indigo, and violet. On the red end of the spectrum, the waves have a lower frequency and a longer wavelength, while on the violet end the waves have a higher frequency and shorter wavelength.
But the visible part is only a fraction of the whole spectrum. The order of the whole electromagnetic spectrum is Radio, Microwaves, Infrared, then Visible light, Ultraviolet, X-rays and Gamma rays. In the spectrum, the frequency increases from radio waves to gamma rays and the wavelength decreases from radio waves to gamma rays. Additionally, the spectrum is a continuous spectrum, meaning the cut-off point between one type of wave and another is unclear. |
| How do electromagnetic waves travel? | Electromagnetic waves can travel through a vacuum e.g. space because they do not need a medium to travel in. When electromagnetic waves travel in a vacuum they all travel at the same speed of 3 x 10^8m per second. |
| What do different materials do with electromagnetic waves? | Different materials absorb, transmit or reflect electromagnetic waves, and what happens to the waves depends on the wavelength e.g. microwaves are absorbed by food containing water molecules, although they are reflected from metals, while light waves are absorbed by black surfaces and reflected from shiny, metallic surfaces. |
| What is a refraction? | A refraction is a change in the direction of a wave at a boundary, and the direction of a wave can be changed by changing the speed of the wave, which happens as the wave moves from one medium to another. |
| How does refraction happen when a light ray passes through a glass box? | When a light ray passes from the air into the glass the velocity of light decreases (the light waves slow down). This causes the direction of the waves to change. A change that can be drawn by drawing the ‘normal’ (a dotted line) perpendicular to the surface of the glass.
As the light wave slows down it bends towards the normal. Now the light waves pass through the glass block.
And when the light waves pass back into the air their velocity increases. When waves speed up they bend away from the normal. And this change in the bend causes the object to appear to have shifted position.
This process is refraction and can happen when any wave changes speed and passes from one medium to another. |
| When will the direction of a wave not change? | When waves enter or leave the medium at right angles to the surface, along the normal, they do not change direction. |
| What is a wavefront? | The wavefront is an imaginary line that connects all the same points in a set of waves e.g. a set of symmetrically aligned transverse waves could have a wavefront connecting their peaks, or troughs. Wavefronts make it easier to visualise many waves moving together. |
| How can wavefronts be used to explain why waves change direction when passing from one medium to another. | Light waves are about to move from air into glass. When the first wavefronts move into the glass they slow down and become closer together, making the wavelength smaller. This causes the waves to change direction towards the normal, so they refract. Then when the waves speed up, they change direction away from the normal, while spreading apart making the wavelength larger.
While when wavefronts are at right angles to the normal the waves slow down as they enter the glass, but the whole wavefront slows down at the same time. The waves, therefore, do not change direction. |
| What is a Leslie’s cube used to do? | A Leslie’s cube can be used to find how much infrared is emitted from different surfaces. Leslie’s cubes have four different surfaces: a shiny metallic surface, a white surface, a shiny black surface, and a matt black surface. |
| How do you measure the emittance of infrared by different surfaces? | First, fill the Leslie’s cube with hot water. Then point an infrared detector at each of the four surfaces. Record the amount of infrared emitted.
The distance between the Leslie’s cube and the infrared detector should be kept the same. This ensures a repeatable measurement.
At the end, the infrared practical will show the matt black surface emits the most radiation. The shiny black surface and the white surface emitted less radiation. While the shiny metallic surface emitted the least infrared radiation. |
| What can be used instead of an infrared detector? | Instead of an infrared detector, a thermometer with a black-painted bulb can be used. Although the resolution of the thermometer is less than the infrared detector, given that the resolution is the smallest change that can be detected. |
| How can you measure the absorbance of infrared by different surfaces? | To measure the absorbency of infrared set up an infrared heater with two metal plates on both sides. The inner side of the one plate is painted with shiny metallic paint, and the other with black matt paint. And the outside of the plates has a drawing pin attached using Vaseline.
Now switch on the heater and start timing.
The temperature of the metal plates will increase as they absorb infrared. Record the time it takes for the Vaseline to melt and the drawing pins to drop off.
Finally, the drawing pin will fall off the matt black plate first because matt black surfaces absorb more infrared than shiny metallic surfaces. Therefore black matt surface better absorbs infrared than the shiny metallic surface that tends to reflect infrared. |
| How are electromagnetic waves generated? | When electromagnetic waves are generated or absorbed changes take place in atoms or in the nuclei of atoms. E.g. in lithium when atoms are heated an electron will move to a higher energy level, and when it returns to its original energy level it will generate an electromagnetic wave.
Changes made to the nucleus can also produce other electromagnetic waves e.g. gamma rays. Gamma rays can be emitted from the nucleus of radioactive atoms. This causes the nucleus to have less energy than it initially had. |
| Why are ultraviolet, X-rays and gamma rays dangerous to the human body? | Ultraviolet, X-rays and gamma rays are dangerous to the human body because ultraviolet waves increase the risk of skin cancer and cause the skin to age prematurely. While x-rays and gamma rays are ionising radiation so they knock electrons off atoms when they are absorbed. This can cause mutations of genes, increasing the risk of skin cancer. Although the effect of radiation depends on the dose, that is measured in sieverts (Sv) or millisieverts (mSv). |
| How can radio waves be produced? | Radio waves can be produced when electrons oscillate (more backwards and forwards) in electrical circuits. Then when radio waves are absorbed e.g. by an electrical circuit in an aerial. The electrons in the transmitted and aerial oscillate. And this creates an alternating current with the same frequency as the radio waves. |
| What are radio waves, microwaves, and infrared waves used to do? | Radio waves are used to transmit radio waves and terrestrial TV signals (TV received through an aerial). Radio waves have these uses because they can travel long distances before being absorbed e.g. by buildings and trees. Longer wavelength radio waves can also spread out between trees. Additionally, radio waves reflect off the ionosphere, which is a layer of charged particles in the atmosphere. And this allows radio waves to be sent from very long distances around the earth.
Microwaves are used to heat food. This is because most foods contain a lot of water molecules and water molecules absorb the energy of microwaves. This energy then allows the temperate of the food to increase. Microwaves are also used to communicate with satellites in space. This is because microwaves can pass through the earth’s atmosphere without being reflected or refracted.
Infrared waves are used to cook food in ovens and are emitted by electrical heaters. Infrared waves have these uses because the energy of Infrared is easily absorbed by the surface of objects e.g. the infrared from a heater is absorbed by objects in the room, making the room warmer. Infrared is also used in Infrared cameras e.g. to check buildings for heat losses. |
| What are visible light, ultraviolet X-rays and gamma rays used in? | Visible light is used in communication using fibre optics. Optical fibres are very thin strands of glass. Pulse of light can be transferred down these fibres and these pulses can be used to carry information. Optical fibres are used to carry telephone and cable TV signals. This is especially useful because visible light has a short wavelength, so it can carry a great deal of information.
Ultraviolet waves are used in energy-efficient lightbulbs. As ultraviolet waves have a short wavelength they carry more energy than visible light. And this energy of ultraviolet is absorbed by the internal surface of the bulb and converted into visible light. This requires much less energy than a normal light bulb. Ultraviolet is also used in suntanning e.g. using a tanning bed. Although ultraviolet increases the risk of skin cancer and causes the skin to age prematurely.
X-rays and gamma rays are used in medical imaging e.g. X-rays can be used to detect broken bones, while gamma rays are used to detect cancers. Both X-rays and gamma rays are very penetrative; they easily pass through body tissue. Although X-rays are absorbed by bones so they can be seen in x-ray images. Both X-rays and gamma rays can also be used in medical treatments e.g. to treat cancer. |
