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Electricity and movement

What is the connection between electricity and movement?


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:

a fan converts electrical energy into kinetic energy

a speaker converts electrical energy into sound energy

a kettle converts electrical energy into heat energy

How is electrical energy created in the first place?


How is electrical energy produced?

Most methods of producing electricity involve converting movement (i.e. kinetic energy) into electrical energy.

How does this key energy transfer take place?

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.


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.

Creating electricity from movement

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.

This is called electromagnetic induction. It was discovered by Michael Faraday, a British chemist and physicist, in 1831.


Electromagnetic induction


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?

The speed of the magnet – the faster it moves, the larger the current.

The strength of the magnet – the stronger the magnet, the larger the current.

The number of turns in the coil – the more turns in the coil, the larger the current.


How can motion produce a current?


Electrical power is the rate at which an electrical appliance uses electrical energy. All appliances have a power rating.

What is electrical power?

Power is measured in watts (W). 1000 watts = 1 kilowatt (kW). 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.


Power is measured in watts (W) or kilowatts (kW).

Current is measured in amps (A).

Voltage is measured in volts (V).

What are the units of power, current and voltage?

What is the formula for electrical power?

power = current x voltage

P = I x V

In electrical devices, power can be calculated using the formula:


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…

…which gives the formula…

I =P V

Can I use a formula triangle?

x


A filament bulb has a potential difference of 200 V across it and a current of 0.2 A running through it.

How is power calculated?

At what power is the filament bulb operating?

= 40 W

= 0.2 A x 200 V

P = IV


Electrical power – calculations


Power is measured in kilowatts (kW) 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

Example:

How many units of electricity is 17.6 kWh? 17.6 units

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

Calculating the units of electricity

= 1 kilowatt hour (kWh)


Electricity costs money, which is why every home has an electricity meter.

The units of electrical energy are called kilowatt hours (kWh).

How is electricity paid for?

The cost of an electricity bill is calculated from the number of units used.

The meter records how much electricity is used in a house in units of electrical energy.


The cost of electricity is the number of units of electrical energy multiplied by the cost per unit.

Example:

How much would 10 units of electricity cost at a price of 9p per unit?

cost = 10 units x 9 p/unit

cost = number of units x cost per unit

How much does electricity cost?

= 90 p


A kettle uses 45.2 kWh of energy.If electricity costs 10 p per unit, how much does it cost to use the kettle?

Number of units:

Cost of electricity:

Buying electricity – example

= 45.2 units

number of units of electricity = number of kilowatt hours

= 452 p or £4.52

= 45.2 units x 10 p / unit



An iron that operates at a power of 3 kW for 4 hours uses electricity that costs 8p per unit. How much does it cost for the electricity used by the iron in that time?

Number of units:

Cost of electricity:

Buying electricity – example

= 12 units

= 12 kWh

= 3 kW x 4 h

number of units of electricity = number of kilowatt hours

= 96p

= 12 units x 8 p / unit



Buying electricity – calculations


generator – A machine that converts kinetic energy into electrical energy by induction.

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.

kilowatt hour – The unit of electrical energy.

power – The rate at which energy is transferred.

watt – The unit of power. 1 watt = 1 joule of energy transferred every second.

Glossary


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Multiple-choice quiz

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