# Physics P3

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## Equations

• Energy transferred = Power x Time
• (in joules)                  (in W)     (in s)
• Energy transferred = Power x Time
• (in Kwh)                     (in KW)  (in hours)
• Cost = Number of Kwh x Cost per Kwh
• Power = Voltage x current
• (in W)     (in volts)  (in amps)
• Efficiency = Energy usefully transferred
•                     Total energy supplied               x 100%
• (To work out the efficiency of energy transfers in a sankey diagram is):
• Efficiency = Useful energy output
•                         Energy input
• Payback time = initial cost
•                         annual saving
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## Electrical energy

• Power is the rate of energy transfer. The power of an appliance tells you how fast it transfers energy from the charge passing through it. Power is usually measured in watts or kilowatts (1Kw= 1000 W). A power rating of 100 W means it transfers 100 joules of energy every second.
• Energy is measured in joules.
• A kilowatt- hour is the amount of electrical energy converted by a 1kW appliance left on for 1 hour.
• Electrical appliances transfer energy from the charge passing through them but not all of the energy is used usefully - some always gets wasted (often as heat or sound).
• Voltage is the energy per electron/ the amount of push.
• Current is the speed of flow of the electrons/ electrons per second.
• The voltage in a home mains supply is 230 V.
• Efficiency = A measure of what percentage of energy going into an appliance is usefully transferred.
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## Saving energy

• Reducing energy usage begins at home.

- A lot of the things you can do to save energy at home invlove stopping heat escaping (the less energy you waste, the less you need to use in the first place).

1. Install cavity wall and loft insulation, double glazing and drought proofing reduces the heat lost through gaps in walls, ceilings, windows and around doors.

2. Buy a fibreglass wool hot water tank jacket and thick curtains. This can also reduce heat loss.

3. You can also reduce the amount of electricity you use by buying efficient appliances and energy saving light bulbs, as well as switching things off when you are not using them. Washing clothes at lower temperatures and turning down the heating can also help.

The Government can encourage people to save energy too. E.g. By offering grants for better home insulation, running schemes to trade in old boilers for more efficient ones and by improving public transport. They can help control energy use on a national scale too. E.g. by investing in alternative energy sources, improving recycling services and making laws to ensure new housing and businesses are energy efficient.

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## Energy sources and power stations

• We use different energy sources to generate electricity.
• Electricity is a convenient way to supply Energy.
• Electricity is a secondary source because it is produced using other energy sources. E.g. coal, nuclear fuel, wind power are primary sources.
• Electricity is convenient as it can be easily transmitted over long distances via the national grid and can be used in many different ways.
• There are lot of different types of energy sources which are either renewable or non-renewable.

- Non-renewable sources = They have a limited supply, they all do damage to the environment, they currently provide most of our energy.

- Renewable sources = They are an unlimited supply, they do damage the environment but in less nasty ways than no-renewables. They don't provide much energy and can be unreliable if they depend on the weather.

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## Power stations and how they work

1. Thermal power stations:

• Energy is released from the fuel (usually by burning in a boiler and used to generate steam).
• The steam turns a turbine.
• A generator converts the movement of the turbine (kinetic energy) into electricity.

2. Nuclear power stations:

• Energy is released from the nuclear fuel (e.g. uranium) by nuclear fission.
• The heat energy heats water to make steam.
• The steam turns the turbine.
• A generator converts the movement of the turbine (kinetic energy) into electricity.

3. Hydroelectric power:

• Water is stored in the reservoir above the turbines using a dam.
• Gravity causes the water to rush through the turbines.
• A generator converts the movement of the turbines (kinetic energy) into electricity.
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1. Nuclear reactions release a lot more energy than chemical reactions.

2. A nuclear power station does not produce CO2 when making electricity.

3. Nuclear fuel is relatively cheap.

1. Nuclear power stations produce radioactive waste - this is dangerous and is difficult to dispose of as it emits ionising radiation and stays radioactive for a long time. Radioactive waste can put people at risk:

- Contamination = radioactive material on yo or in you (internal/ external).

2. Nuclear power stations take the longest time of all the power stations to start up. The overall cost is high due to the cost of the power plant and final decommissioning.

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## How does a generator work?

In order to generate electricity, various equipment is required such as a coil of wire, a magnet and to complete the circuit it is required to have an ammeter or a light bulb. For this process of generating electricity, the coil of wire and the magnet need to go into one another and move relative to each other, in order for kinetic energy to make the electrons within the coil have a huge voltage and therefore make the light bulb light. Electrical energy goes in and kinetic energy comes out. There are various factors which produce a brighter beam of light or more electrons per second; current. This process has an alternating current. For example, add more coils, increase he speed of the magnet and the strength. This process is called electromagnetic induction.

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