electricity

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  • Created by: clo_R
  • Created on: 24-05-16 14:20

units

Units needed for exam

Unit of current: ampere (A)
Unit of charge: coulomb (C)
Unit of energy: Joule (J) 
Unit of resistance: ohm (Ω) 
Unit of time: second (s) 
Unit of voltage or potential difference: volt (V)
Unit of Power: watt (W) 

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electrical symbols

Circuit symbols of open switch, closed switch, lamp, voltmeter, resistor, variable resistor, diode, light emitting diode, battery, cell, ammeter, fuse, thermistor and light dependant resistor. (http://a.files.bbci.co.uk/bam/live/content/zp8h34j/large)

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electrical hazards

There are lots of ways in which we can be electrocuted including:

  • touching frayed electrical cables
  • long or overheating cables
  • damaging or incorrectly wired plugs
  • allowing water or wet objects to enter plug sockets or touch frayed cables
  • pushing metal objects into plug sockets

Plug

The inside of a plug showing the positioning of the earth, neutral and live wires, as well as the fuse and cable grip. (http://a.files.bbci.co.uk/bam/live/content/zbxb87h/small)

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Electrical power

The power of an electrical appliance can be calculated from the current that lows through it and the potential difference across it.

power = current x voltage

P = I x V

where:

P is the power in watts, W

I is the current in amperes (amps), A

V is the potential differences in volts, V

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electrical energy

For a given amount of electrical charge that oves, the amount of energy transferred increases as the potential difference increases

calculating energy transferred:

energy = current x voltage x time

E= I x V x t

where:

E is the energy transferred in joules, J

I is the current in amperes, A

V is the potential differences in volts, V

t is the time in seconds, S

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cost of electricity

Electricity meters measure the number of units of electricity used in a home or other building. The more units used, the greater the cost. The cost of the electricity used is calculated using this equasion:

total cost = number of units x cost per unit

number of units used can be calculated using this equasion:

Units (kWh) = power (kW) x time (h)

total cost = power (kW) x time 9h) x cost per unit

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charge and current

electric current is the rate of flow of electric charge. No current can flow if the circuit is broken- for example, when a switch is open.

An electric current flows when electrons move through a conductor, such as a metal wire. metals arre good conductors of electricity.

Electricity passes through metallic conductors as a flow of negatively charged electrons. The electrons are free to move from on atom to another. We call them a sea of delocalised electrons.

Loose electrons form a sea of delocalised electrons. (http://a.files.bbci.co.uk/bam/live/content/zmr2n39/medium)

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calculating current

The size of an electrical current shows the rate of flow of electrical charge. You can caluclate the size of a current using this equasion:

current in amps = charge in coulombs / time in seconds

I = Q / t

Where:

I is the current in amps, A

Q is the charge in coulombs, C

t is the time in seconds, S

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Measuring potential difference (voltage) and curre

potential difference across an electrical component is needed to make an electric current flow in it. Potential difference is often called voltage. it is also known as electromotive force. 

Measuring potential difference

  • measured  in volts, V
  • the potential difference across a component in a circuit is measured using a voltmeter
  • a voltmeter mus be connected in parallel with the component

Circuit with a cell, switch and lamp. A voltmeter is connected in parallel with the lamp. (http://a.files.bbci.co.uk/bam/live/content/zxcmsbk/small)

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Measuring potential difference (voltage) and curre

Measuring current

  • current is measured in amps
  • the current flowing through a component in a circuit is measured using an ammeter
  • the ammeter must be connected in series with the component

Circuit with a cell, switch, lamp and ammeter connected in series. (http://a.files.bbci.co.uk/bam/live/content/z64xfg8/small)

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