4.09 practical: investigate thermal energy transfer by conduction, convection and radiation
2.23 practical: investigate how insulating materials can be charged by friction
- Hold polythene rod and cloth next to up small pieces of paper one at a time, observe.
- Now rub the rod with the cloth
- Again hold close to small pieces of paper, observe.
- Turn on a tap so a thin stream of water is flowing
- Hold the rod about 1cm away from the water just below the nozzle, observe
- Repeat with different material rods and cloths
5.06 understand how the pressure at a point in a gas or liquid at rest acts equally in all directions
Pressure in liquids:
Pressure in liquids acts equally in all directions as long as the liquid is not moving.
4.10 explain ways of reducing unwanted energy transfer, such as insulation
A good insulating material is a poor conductor that contains trapped air, e.g. foam, feathers, glass fibre. Being a poor conductor (non-metal) prevents heat transfer by conduction and the trapped air prevents convection currents.
4.08 explain how emission and absorption of radiation are related to surface and temperature
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– Light, shiny surfaces are good reflectors of IR and so are poor at absorbing it. – Dark, matt surfaces are poor reflectors and good at absorbing IR. – This means that placed next to a heat source, a dark object would heat up faster than a light one. – Dark matt surfaces are also best at emitting IR. This means that a hot object with a light shiny surface will emit less IR than a dark matt object at the same temperature. – Hotter objects emit more IR per second. The type of EM wave emitted also changes with temperature – the higher the temperature the higher the frequency of EM wave emitted. |
4.06 describe how thermal energy transfer may take place by conduction, convection and radiation
Conduction is the transfer of thermal energy through a substance by the vibration of the atoms within the substance. Metals are good conductors because they have free electrons that can move easily through the metal, making the transfer of energy happen faster.
Convection occurs in a liquid or gas. These expand when heated because the particles move faster and take up more volume – the particles remain the same size but become further apart. The hot liquid or gas is less dense, so it rises into colder areas. The denser, colder liquid or gas falls into the warm areas. In this way, convection currents are set up which transfer heat from place to place.
Thermal radiation is the transfer of energy by infrared (IR) waves. These travel very quickly in straight lines.
3.29 understand how the loudness of a sound relates to the amplitude of vibration of the source
The greater the amplitude the louder the sound. Bigger vibrations of a sting mean more energy is being put in so more energy out as sound waves.
3.28 understand how the pitch of a sound relates to the frequency of vibration of the source
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High frequency means high pitch. If a string vibrates with a higher frequency then the note sounds higher. |
3.26 understand how an oscilloscope and microphone can be used to display a sound wave
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With the microphone plugged into the oscilloscope and a sound incident on the microphone, the microphone will transfer the sound into an electrical signal which the oscilloscope can display .The x axis show the time base which can be adjusted for example 2ms for 1 square so time period and frequency can be calculated from this, along the y axis voltage is displayed as the wave is converted into an electrical signal this means amplitudes can be compared. |
3.24 know that the frequency range for human hearing is 20–20 000 Hz
the frequency range for human hearing is 20–20 000 Hz
3.08 explain why there is a change in the observed frequency and wavelength of a wave when its source is moving relative to an observer, and that this is known as the Doppler effect
Doppler Effect:
- When a car is not moving and its horn sounds, the sound waves we receive are a series of evenly spaced wavefronts.
- If a car is moving, wavefronts of the sound are no longer evenly spaced.
- Ahead of the car wavefronts are compressed as the car is moving in the same direction as the wavefronts. This creates a shorter wavelength and a higher frequency.
- Behind the car wavefronts are more spread out as the car is moving away from the previous wavefronts. This creates a longer wavelength and a lower frequency.
2.28 explain some uses of electrostatic charges, e.g. in photocopiers and inkjet printers
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Paper is charged negatively in certain regions. Then positively charged paint droplets are sprayed onto the paper and attracted to the negative regions of the paper giving the desired image. |
