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Electricity and movement What is the connection between electricity and movement? 3 of 26 © Boardworks Ltd 2006

Energy transfer in the home Electricity in the home is an essential source of energy for many appliances. In all electrical appliances, electrical energy is transferred to other types of energy, for example: l a fan converts electrical energy into kinetic energy l a speaker converts electrical energy into sound energy l a kettle converts electrical energy into heat energy How is electrical energy created in the first place? 4 of 26 © Boardworks Ltd 2006

How is electrical energy produced? Most methods of producing electricity involve converting movement (i. e. kinetic energy) into electrical energy. Coal, oil, gas and nuclear power stations convert kinetic energy from high-pressure steam into electrical energy. Wind turbines convert kinetic energy from wind into electrical energy. How does this key energy transfer take place? 5 of 26 © Boardworks Ltd 2006

Creating electricity from movement Electricity is created from the movement of a wire in a magnetic field, or the movement of a magnetic field within a coil of wire. This is called electromagnetic induction. It was discovered by Michael Faraday, a British chemist and physicist, in 1831. In power stations and wind turbines, induction takes place in generators. Here, a large turbine spins a magnet around within a set of coils, inducing a large electrical current. 6 of 26 © Boardworks Ltd 2006

Electromagnetic induction 7 of 26 © Boardworks Ltd 2006

Factors affecting induction Electricity is induced when a magnet moves inside a coil of wire. When the magnet stops moving, so does the electrical current. What factors affect the size of the electrical current induced? l The speed of the magnet – the faster it moves, the larger the current. l The strength of the magnet – the stronger the magnet, the larger the current. l The number of turns in the coil – the more turns in the coil, the larger the current. 8 of 26 © Boardworks Ltd 2006

How can motion produce a current? 9 of 26 © Boardworks Ltd 2006

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What is electrical power? Electrical power is the rate at which an electrical appliance uses electrical energy. All appliances have a power rating. Power is measured in watts (W). 1000 watts = 1 kilowatt (k. W). 1 watt of power means that 1 joule of energy is used every second. Appliances that need to create heat, such as washing machines, cookers, hair dryers and kettles, usually use the most power. TVs, radios and computers usually use the least amount of power. 11 of 26 © Boardworks Ltd 2006

What is the formula for electrical power? In electrical devices, power can be calculated using the formula: power = current x voltage P = Ix. V What are the units of power, current and voltage? l Power is measured in watts (W) or kilowatts (k. W). l Current is measured in amps (A). l Voltage is measured in volts (V). 12 of 26 © Boardworks Ltd 2006

Can I use a formula triangle? A formula triangle helps you to rearrange a formula. The formula triangle for P = IV is shown below. Cover up whatever quantity you are trying to find to leave the calculation required. So to find current (I), cover up I… x 13 of 26 …which gives the formula… P I = V © Boardworks Ltd 2006

How is power calculated? A filament bulb has a potential difference of 200 V across it and a current of 0. 2 A running through it. At what power is the filament bulb operating? P = IV = 0. 2 A x 200 V = 40 W 14 of 26 © Boardworks Ltd 2006

Electrical power – calculations 15 of 26 © Boardworks Ltd 2006

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Calculating the units of electricity The amount of electrical energy (i. e. the amount of electricity) used by an appliance depends on its power and how long the electricity is used for. electrical energy = power x time Power is measured in kilowatts (k. W) and the time is measured in hours (h), so what are the units of electricity measured in? 1 unit of electricity = 1 unit of electrical energy = 1 kilowatt hour (k. Wh) Example: How many units of electricity is 17. 6 k. Wh? 17. 6 units 17 of 26 © Boardworks Ltd 2006

How is electricity paid for? Electricity costs money, which is why every home has an electricity meter. The meter records how much electricity is used in a house in units of electrical energy. The units of electrical energy are called kilowatt hours (k. Wh). The cost of an electricity bill is calculated from the number of units used. 18 of 26 © Boardworks Ltd 2006

How much does electricity cost? The cost of electricity is the number of units of electrical energy multiplied by the cost per unit. cost = number of units x cost per unit Example: How much would 10 units of electricity cost at a price of 9 p per unit? cost = 10 units x 9 p/unit = 90 p 19 of 26 © Boardworks Ltd 2006

Buying electricity – example A kettle uses 45. 2 k. Wh of energy. If electricity costs 10 p per unit, how much does it cost to use the kettle? Number of units: number of units of electricity = number of kilowatt hours = 45. 2 units Cost of electricity: cost = number of units x cost per unit = 45. 2 units x 10 p / unit = 452 p or £ 4. 52 20 of 26 © Boardworks Ltd 2006

Buying electricity – example An iron that operates at a power of 3 k. W for 4 hours uses electricity that costs 8 p per unit. How much does it cost for the electricity used by the iron in that time? Number of units: number of units of electricity = number of kilowatt hours = 3 k. W x 4 h = 12 k. Wh = 12 units Cost of electricity: cost = number of units x cost per unit = 12 units x 8 p / unit = 96 p 21 of 26 © Boardworks Ltd 2006

Buying electricity – calculations 22 of 26 © Boardworks Ltd 2006

Glossary l generator – A machine that converts kinetic energy into electrical energy by induction. l induction – Generating a current in a wire by moving the wire in a magnetic field, or by moving a magnet inside a coil of wire. l kilowatt hour – The unit of electrical energy. l power – The rate at which energy is transferred. l watt – The unit of power. 1 watt = 1 joule of energy transferred every second. 24 of 26 © Boardworks Ltd 2006