# Energy and power in circuits

• Created by: jp3louis
• Created on: 20-02-16 19:26

## How energy is transferred in cells and other sourc

Energy is transferred from cells and other sources.

Anything which supplies electricity is also supplying energy.

Cells, batteries and generators all transfer energy to components in the circuit.

Motion: motors / Light : light bulbs / Heat: Hair dryers or kettles / Sound: speakers

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## Resistors

Resistors provide heat when a current flows through them.

Whenever current flows through anything with electrical resistance, the electrical energy is converted into heat energy.

The more current that flows, the more heat is produced.

A bigger voltage means more heating because it pushes more current through.

Filament bulbs work by passing a current through a very thin wire, heating it up so much that it glows. They waste alot of energy as heat.

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## Appliances and efficiency

If an appliance is efficient it wastes less energy.

You can buy more energy efficient appliances.

These more energy efficient appliances transfer more of their total energy output to useful energy.

Less energy is wasted in power saving lamps such as compact flurescent lamps and light emitting diodes than in ordinary bulbs.

They do cost more to buy but over time money is saved on electricity bills.

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## Power of appliances

The total energy transferred by an appliance depends on how long the appliance is on and what power it uses. The power of an appliance is the energy that it uses per second.

The equation for it is:

Energy transferred = Power X Time or E = P X T

Example question

If a 2.5 KW kettle is on for 5 minutes, the energy transferred by the kettle in this time is 300 X 2500 = 750000 J = 750 kj

We use the number 300 as 5 minutes = 300 seconds

2.5 into W is 2500

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