- Infrared radiation is energy transfer by electromagnetic waves. Every object emits infrared radiation.
- The hotter the object is, the more infrared radiation it emits in a given time.
The electromagnetic spectrum:
- Radio waves
- Infrared radiation
- Visible light
- Gamma rays
- Electromagnetic waves are electric and magnetic waves that travel through space.
- Short wavelength infrared radiation from the Sun can pass through glass to warm the inside of a greenhouse.
- The radiation from these objects is trapped because the objects emit longer wavelengths that can't pass through the glass.
- Dark, matt surfaces emit more infrared radiation than light, shiny surfaces.
- Dark, matt surfaces absorb more infrared radtion than light, shiny surfaces.
- Light, shiny surfaces reflect more infrared radiation than dark matt surfaces.
- Flow, shape, density and volume are the properties used to describe each state of matter.
- The particles in a solid are held next to each other in fixed positions.
- The particles in a liquid move about at random and are in contact with each other.
- The particles of a gas move about randomly and are much further apart than particles in a liquid or a solid.
- A fluid is a substance with free moving particles, so can be used to describe a liquid or a gas.
- Metals are the best conductors of energy as they contain free electrons. These move about at random, so if one end of a metal rod is heated, the electrons will collide with each other and diffuse, transfering the energy across the metal.
- Materials such as wool and fibreglasses are the best insulators.
- Non-metals are poor conductors because they do not contain free electrons, and often have trapped air pockets that make transfer of heat only avaliable through radiation.
- Convection is the circulation of a fluid (liquid or gas) caused by heating it. It only occurs in fluids.
- Heating a fluid makes it less dense, as the particles are moving around more so are taking up more space, so it rises and causes circulation.
- Hot fluids rise.
- Evaporation is when a liquid turns into a gas, condensation is when a gas turns into a liquid.
- Cooling by evaporation of a liquid is due to the faster-moving molecules escaping from the liquid.
- Evaporation can be increased by increasing the surface area of the liquid, by increasing the liquid's temperature, or by creating a draught of air across the liquid's surface.
- Condensation on a surface can be increased by increasing the area of the surface or reducing the temperature of the surface.
The rate of energy transferred to or from an object depends on:
- The shape, SIZE or type of the object.
- The m a t e r i a l s the object is in contact with.
- The temperature difference between the object and its surroundings.
- The rate of temperature change of a substance when it is heated depends on the energy supplied to it, its mass and its specific heat capacity.
- Specific heat capacity = The energy needed or transferred to 1kg of the substance to raise its temperature by 1 degree C.
- Storage heaters use off-peak electricity to store energy in special bricks that're heated and slowly release that heat into their environments.
Energy transfer from our homes to the local environment can be reduced by fitting:
- Loft insulation
- Cavity wall insulation
- Double glazing
- Draught proofing
- Aluminium foil behind radiators
- U-Value is the energy that passes through one square metre of material when the temperature difference across it is 1 degree C.
- The lower the U-Value, the more effective the material is as an insulator.
- Solar heating panels don't require fuel to heat water, as they harness the sun's rays. However, they are very expensive to buy and install, as well as the fact there may not always be sufficient sunlight to heat the water.
- Chemical energy = energy stored in fuel (including food). Is released when chemical reactions take place.
- Kinetic energy = the energy of a moving object.
- Gravitational potential energy = energy of an object due to its position.
- Elastic potential energy = the energy stored in a springy object when we stretch/squash it.
- Electrical energy = energy transferred by an electric current.
- When an object falls and gains speed, its gravitational potential energy decreases and its kinetic energy increases.
- Energy cannot be created or destroyed, only transferred to a different form of energy.
- This is called conservation of energy. This applies to all energy changes.
- Useful energy is energy that is tranferred to the place we want it and the form we need it.
- Wasted energy is energy that is not useful energy.
- Useful energy and wasted energy both end up being transferred to the surroundings, which become warmer.
- As energy spreads out, it gets more and more difficult to use for further energy transfers.
- Weight is measured in Newtons (N). 1kg = 10N on the Earth surface.
- Energy is measured in Joules (J). The energy needed to lift 1N by a height of 1m is 1J.
- The efficiency of a device = useful energy transferred by the device / total energy supplied to the device (x 100%).
- No machine can be more than 100% efficient, as energy can't be created (or destroyed).
- Measures to make machines more efficient include reducing friction, air resistance, electrical resistance and noise due to vibrations.
Electrical appliances can transfer electrical energy into useful energy at the flick of a switch. This includes in:
- Making objects move (using an electric motor e.g. a blender)
- Creating sound
- Creating visual images
An electrical appliance is designed for a particular purpose, and should waste as little energy as possible.
- Power is rate of transfer of energy.
- P = E/t
- Efficiency = useful power out / total power in } (x 100%)
- 1 watt is a rate of transfer of energy of 1J/s.
- 1 kilowatt = 1000 watts = 1000J/s
- The energy supplied to a 1kW appliance for 1 hour is 1 kilowatt-hour (kWh).
- Total cost = number of kWh used x cost per kWh.
- The mains voltage is between 220-230 volts.
- Cost effectiveness means getting the best value for money.
- To compare the cost effectiveness of different appliances, we need to take into account: costs to buy it, running costs and other costs (e.g. environmental costs).
- Electricity generators in power stations are driven by turbines.
- Coal, oil and natural gas are burned to boil water to spin the turbines in fossil fuel power stations.
- Uranium or plutonium are used as the fuel in a nuclear power station. Much more energy is released per kg from uranium or plutonium than from fossil fuel.
- Nuclear fission occurs when unstable atoms split, releasing energy. Because there's so many of these atoms in a core, it gets very hot. This allows us to heat the water for steam.
- Biofuels are renewable sources of energy. Biofuels such as methane and ethanol can be used to generate electricity.
- A wind turbine is an electrical generator on top of a tall tower, where giant blades are turned by the wind. As the wind increases, so does the power.
- Waves generate electricity by turning a floating generator, but pose many problems like spoiling coastlines, the large amount of cable required, and not producing constant supplies of energy.
- Hydroelectricity generators are turned by water running downhill.
- Tidal power stations trap each high tide and then release it back into the sea through turbines to turn the generators.
- Solar cells are flat solid cells that convert solar energy directly into electricity.
- Solar heating panels use the Sun's energy to directly heat water.
- Geothermal energy comes from the energy released by radioactive substances inside the Earth. Water pumped into hot rocks underground produces steam to drive turbines that generate electricity.
- Fossil fuels produce increased levels of greenhouses gases which could cause global warming.
- Nuclear fuels produce radioactive waste, stations could explode releasing harmful substances.
- Wind turbines create sound and visual pollution.
- Tidal barrages and hydroelectric schemes affect the local habitats and creatures.
- Solar cells need to cover large areas to generate large amounts of power.
- Nuclear power releases no greenhouse gases, and there's far more energy released from uranium or plutonium than fossil fuels.
- Renewable sources will never run out, produce acid rain, radioactive waste or greenhouse gases.
- The National Grid's voltage is 132000V or more, as transmitting electricity at a high voltage reduces power loss, making it more efficient.
- Power stations produce lectricity at a voltage of 25000V.
- We use step-up transformers to increase the voltage, and step-down to decrease it.
- The National Grid is a network of cables and transformers that distributes electricity to our homes from distant power stations and renewable energy generators.
- Gas-fire power stations and pumped-storage stations can meet variations in demand.
- Nuclear, coal, and oil power stations can meet base-load demands as they're reliable if not renewable.
- Nuclear power stations, fossil-fuel power stations using carbon capture and renewable energy are all likely to contribute to future energy supplies.
- We use mechanical waves such as sound, water, and waves on springs/ropes. These are vibrations that travel through a medium (substance). These transfer information and energy.
- We use electromagnetic waves such as light, radiowaves and microwaves that can travel through a vacuum without requiring a medium. These also transfer information and energy.
- Transverse waves vibrate at right angles to the direction of energy transfer of the waves. All electromagnetic waves are transverse waves.
- Longitudinal waves vibrate parallel to the direction of energy transfer of the waves. A sound wave is an example of a longitudinal wave.
- Mechanical waves, which need a medium, can be either transverse OR longitudinal waves.
- For any wave, the amplitude is the height of the wave crest or the depth of the wave trough from the position at rest
- Wave frequency is the number of wave crests passing a point per second.
- For any wave, its wavelength is the distance from one wave crest to the next one. This is the same as the distance from one wave trough to the next wave trough.
Speed = Frequency x Wavelength
- The normal at a point on a mirror is a line drawn perpendicular to the mirror.
- The law of reflection states that the angle of incidence = angle of reflection
For a light ray reflected by a plane (flat) mirror:
- The angle of incidence is the angle between the incident ray and the normal.
- The angle of reflection is the angle between the reflected ray and the normal.
- Refraction is the change of direction of waves when they travel across a boundary.
- When a light ray refracts as it travels from air into glass, the angle of refraction is less than the angle of incidence.
- When a light ray refracts as it travels from glass into air, the angle of refraction is more than the angle of incidence.
- Diffraction is the spreading out of waves when they pass through a gap or round the edge of an obstacle.
- The narrower a gap is, the greater the diffraction is.
- If radio waves do not diffract enough when they go over hills, radio and TV reception will be very poor.
- If a ultrasound transmitter is too narrow, the waves will spread out too much and make the image very blurry.
- The frequency range of the normal human ear is from about 20Hz to about 20,000Hz.
- Sound waves are vibrations that travel through a medium (substance). They cannot travel through a vacuum, e.g. space.
- Echoes are due to sound waves relected from a smooth, hard surface.
- Sound travels through air at about 340m/s.
- The pitch of a noise increases if the frequency of the sound waves increases.
- The volume of a note increases if the amplitude of the sound waves increases.
- Vibrations created in an instrument when it is played produce sound waves.
- The wave speed equation is used to calculate the frequency or wavelength of electromagnetic waves.
Wave Speed (m/s) = Frequency (Hz) x Wavelength (m)
- White light contains all the colours of the visible spectrum.
- Infrared radiation is used for carrying signals from remote handsets and inside optical fibres, and can damage or kill skin cells because it heats them up.
- Microwaves carrying satellite TV programmes and mobile phone calls.
- Radio waves are used for radio and TV broadcasting, radio communications and mobile phone calls.They can be harmful as they can cause internal heating.
- Microwaves are used for satellite TV signals.
- Further research is needed to evaluate whether or not mobile phones are safe to use, due to the electromagnetic waves released and properties those waves have.
- Optical fibres are very thin transparent fibres that are used to transmit signals by light and infrared radiation.
Radio waves of different frequencies are used for different purposes because the wavelength of waves affect:
- How far they go
- How much they can spread
- How much information they can carry
The Doppler Effect is the change in wavelength due to the motion of the source of the waves:
- The red-shift of a distant galaxy is an example of this, moving to longer wavelengths (the colour red has a longer wavelength than blue) as the galaxy is moving away from us.
- The faster the galaxy is moving away, the greater its red-shift is.
- All the galaxies show a red-shift, which scientists believe shows that the universe is expanding.
- Scientists believe the universe started with the Big Bang, a massive explosion from a very small point, and that ever since the universe has been expanding.
- CMBR (Cosmic Microwave Background Radiation) is the electromagnetic radiation created just after the Big Bang, and can currently only be explained but the Big Bang Theory.