ElectricityElectricity

ContentsContents CircuitsCircuits Current in a Series CircuitCurrent in a Series Circuit Current in a Parallel CircuitCurrent in a Parallel Circuit Voltage in a Series CircuitVoltage in a Series Circuit Voltage in a Parallel CircuitVoltage in a Parallel Circuit Resistance through ComponentsResistance through Components Charge in CircuitsCharge in Circuits Energy in CircuitsEnergy in Circuits Mains ElectricityMains Electricity National GridNational Grid Wiring a PlugWiring a Plug Fuses and SafetyFuses and Safety Cost of ElectricityCost of Electricity

CircuitsCircuits Current, ICurrent, I flow of electrons around the circuitflow of electrons around the circuit

(Amps)(Amps) (how fast the electrons travel around)(how fast the electrons travel around)

Voltage, VVoltage, V Driving force that pushes electronsDriving force that pushes electrons

(Volts)(Volts) (electrical pressure)(electrical pressure)

Resistance, RResistance, R Slows down the electronsSlows down the electrons

(Ohms)(Ohms) (resists the flow of the electrons)(resists the flow of the electrons)

V

I R

Current in a Series CircuitCurrent in a Series Circuit

The current stays the same everywhere in a series circuit

Current here = 5A

Current here = 5A

Current here = 5A

Current here = 5A

Current in a Parallel CircuitCurrent in a Parallel CircuitCurrent here = 9A

Current splits in 3 ways

Current splits in 3 ways

Current splits in 3 ways

Current here = 3A

Current here = 3A

Current here = 3A

The current splits along strands in a parallel circuit

Voltage in a Series CircuitVoltage in a Series Circuit

V

V VVoltage here = 4V

Voltage here = 12V

Voltage here = 4V

The voltage splits along components in a series circuit

Voltage in a Parallel CircuitVoltage in a Parallel Circuit

The voltage stays the same along strands in a parallel circuit

V

V

Voltage here = 12V

Voltage here = 12V

Voltage here = 12V

Resistance Through Resistance Through ComponentsComponents

I

V I

V

I

V

1. Resistor 3. Diode

2. Bulb

Charge in CircuitsCharge in Circuits Electrons travel around a circuit Electrons travel around a circuit electricity electricity Each electron carries energy with itEach electron carries energy with it Each electron has a negative chargeEach electron has a negative charge

In a circuit the total charge, Q, can be calculated In a circuit the total charge, Q, can be calculated by finding how much charge flows in the circuit:by finding how much charge flows in the circuit:

Time, t (secs)Time, t (secs)

Q

I T

Energy in CircuitsEnergy in Circuits Energy, EEnergy, E flow of energy around the circuitflow of energy around the circuit

(Joules)(Joules)

Voltage, VVoltage, V Driving force that pushes electronsDriving force that pushes electrons

(Volts)(Volts) (electrical pressure)(electrical pressure)

Charge, QCharge, Q Charge carried by the electronsCharge carried by the electrons

(Coulombs)(Coulombs)

E

Q V

Mains ElectricityMains Electricity

The UK mains supply is The UK mains supply is 230-240V230-240V Mains electricity is Mains electricity is ACAC (alternating current) (alternating current) The electricity in the mains supply switches direction 50 The electricity in the mains supply switches direction 50

times per second (but this is too fast to see so lights times per second (but this is too fast to see so lights don’t appear to flicker… although they are, 50 times don’t appear to flicker… although they are, 50 times every second!)every second!)

The The larger the currentlarger the current (faster the electrons travel), the (faster the electrons travel), the greater the friction producedgreater the friction produced

Friction produces Friction produces heatheat

This heat is used for kettles, cookers, irons…This heat is used for kettles, cookers, irons…

National GridNational Grid

National GridNational Grid = =

Power station Power station step-up transformer step-up transformer pylons pylons step-down transformer step-down transformer homes homes

Electricity is produced in power stationsElectricity is produced in power stations It is transported along pylons at It is transported along pylons at very highvery high voltage voltage

(400,000V)(400,000V) The higher the voltage, the lower the current…The higher the voltage, the lower the current… and the lower the current the and the lower the current the smaller the heat (energy) smaller the heat (energy)

lossloss

The The high voltage is not safehigh voltage is not safe for domestic use… for domestic use… so the voltage is stepped-down to 230-240Vso the voltage is stepped-down to 230-240V

Wiring a PlugWiring a Plug

LeftbLue (neutral)

Rightbrown (live)

Fuses and SafetyFuses and Safety Live Live wire alternates between +ve and –ve voltagewire alternates between +ve and –ve voltage Neutral Neutral wire is always at 0Vwire is always at 0V EEaarrtthh wire and fuses are there for safety wire and fuses are there for safety

In the case of a fault (earth wire):In the case of a fault (earth wire):

1) live wire touches the metal case1) live wire touches the metal case

2) big current flows through earth wire…2) big current flows through earth wire…

3) … and into the earth3) … and into the earth

In the case of a fault (fuse):In the case of a fault (fuse):

1) surge in current melts the fuses (a thin wire)1) surge in current melts the fuses (a thin wire)

2) the circuit breaks 2) the circuit breaks the supply is broken the supply is broken

Cost of ElectricityCost of Electricity Electricity bills show how many Electricity bills show how many unitsunits of electricity you of electricity you

usedused

1 unit = 1 kilowatt-hour (an amount of energy)1 unit = 1 kilowatt-hour (an amount of energy)

1 kilowatt-hour1 kilowatt-hour = amount of electrical energy used by a = amount of electrical energy used by a 1kW appliance left on for 1 hour1kW appliance left on for 1 hour

Cost = Power x Time x Cost of 1kWhCost = Power x Time x Cost of 1kWh

(kW)(kW) (hrs) (hrs)

NoteNote: 1kW = 1000W, 1hr = 3600secs: 1kW = 1000W, 1hr = 3600secs

SummarySummary

Voltage = Current x ResistanceVoltage = Current x Resistance Series:Series: current stays the samecurrent stays the same

voltage shared between componentsvoltage shared between components Parallel:Parallel: current splits between strandscurrent splits between strands

voltage stays the same between strandsvoltage stays the same between strands Charge = Current x TimeCharge = Current x Time Energy = Charge x VoltageEnergy = Charge x Voltage Mains is AC (230-240V)Mains is AC (230-240V) High voltage = low heat (energy) loss… but is unsafeHigh voltage = low heat (energy) loss… but is unsafe Safety features of plugs are: earth wire, fuseSafety features of plugs are: earth wire, fuse Cost of electricity = Power x Time x Cost of 1kWhCost of electricity = Power x Time x Cost of 1kWh