# Physics unit 1: Whole revision

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## Energy transfer by heating

• Infrared radiation is energy transfer by electromagnetic waves, and all object emit it. The hotter the object, the more infrared given off.
• Dark, matt surfaces emit and absorb infrared quicker than light, shiny surfaces. Light, shiny surfaces reflect more infrared than dark, matt surfaces.
• In a solid, particles are held next to one another and vibrate. In a liquid, the move about and in contact with each other. In a gas, they move apart randomly and are much futher apart than particles in a liquid or gas.
• Metals are good conductors, and materials like wool and fibre glass are good insulators. Conduction in metals is good because it has free electrons transfering energy inside the metal. Non-metals dont have this.
• Convection is the circulation of a fluid (liquid or gas only) caused by heating. Heating it makes it less dense so it rises and circulates.
• Evaporation is when a liquid turns into a gas, and condensation is when a gas turns into a liquid.
• The rate of energy transfer to or from an object depends on its shape, size and type of material and the temperature differences.
• Energy transferred (J) = Mass (kg) x specific heat capacity (J/kg/oC) x temperature change (oC)
• We can minimise the rate of energy transfer out of our homes by having cavity wall insulation, double glazing, draught proofing, fibreglass loft insulation.
• The U-value of something tells us how much energy per second passes through - the lower the U-value the better the material is as an insulator.
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## Using energy

• Light, sound, kinetic, nuclear and electrical are all types of energy. Gravitational potential, elastic potential and chemical potential are all types of stored energy.
• Energy cannot be created or destroyed. Th is the conservation of energy and applies to all energy changes.
• Useful energy is energy in 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 spread out, it gets more and more difficult to use for futher energy transfers.
• Efficiency = useful energy transfer / total energy supplied to the appliance (x100%).
• Machine can be made more efficient by reducing friction, air resistance, electrical resistance and noise due to vibrations.
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## Electrical energy

• An electrical appliance is designed for a particular purpose and should waste as little energy as possible.
• Power is rate of transfer of energy and measured in watts (W). Energy = Joules (J).
• Efficiency = useful power out / total power in (x100%).
• Total cost = number of kWh x cost per kWh.
• Cost effectiveness means getting the best value for money. Payback time is the time taken for an appliance or instillation to profit.
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## Generating electricity

• Electricity generators in power stations are driven by turbines. Uranium or plutonium is used as the fuels in a nuclear power stations.
• Biofuels are renewable sources of energy which can generate electricity.
• Wind and water can be used to generator electricity. Hydroelectricity generators are turned by water running downhill. Tidal power station traps each high tide and uses it to turn generators.
• Solar cells tranfer solar energy directly into electricity, solar heating panels use the Sun's energy to heat water directly.
• Geothermal energy comes from inside the Earth.
• The National Grid uses step-up (increase voltage) and step-down (decrease voltage to 230V) transformers.
• Nuclear, coal and oil power stations can meet base-load demand.
• Nuclear power stations, fossil fuel power stations using carbon capture and renewable energy are all likely to contribute to future energy supplies.
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## Waves

• Transfer waves vibrate at right angles to the direction of energy transfer e.g. electromagnetic.
• Longitudinal waves vibrate parallel to the direction of energy transfer e.g. sound wave.
• Mechanical waves need a medium substance to travel through e.g. tranverse or longitudinal.
• wave speed(v) = frequency(Hz) x wavelength(m)
• Angle of incidence is the angle between the incident ray and the normal.
• Angle of reflection is the angle between the reflected ray and the normal.
• The angle of incidence is equal to the angle of reflection.
• refraction of light is the change in direction of a light ray when it crosses a boundary between two transparent substances.
• If speed is reduced, refractions is towards the normal. If speed is increased, refraction is away from normal.
• Diffraction is the spreading out of waves when they pass through a gap or round the edge of an obstacle. The narrower the gap, the greater the diffraction.
• Sound waves are longitudinal, sound waves need a medium in which to travel. Reflections of sound are called echos.
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## Electromagnetic waves

• The electromagnetic spectrum is gamma rays, X-rays, ultraviolet, visible, infrared, microwaves, radio waves.
• Visible light (green), infrared radiation (yellow), microwaves (red/orange) and radio waves are all used for communication.
• Microwaves are used for satellite TV signals. Optical fibres are very thin fibres that are used to transmit signals by light and infrared radiation.
• Light from different galaxies is called red-shift, it provides us with evidence that the universe is expanding.
• Blue shift is would indicate that a galaxy is moving towards us.
• The doppler effect is the wavelength and frequency of the waves detected by the observer will have changed (shifted) from the original.
• The universe started with the Big Bang: a massive explosion from a very small intial point. The universe has been expanding since the Big Bang.
• Cosmic microwave background radiation (CMBR) is electromagnetic radiation created just after the Big Bang. It can only be explained by the Big Bang Theory.
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