Electricity

Contents Circuits Circuits Current in a Series Circuit Current in a Series Circuit Current in a Parallel Circuit Current in a Parallel Circuit Voltage in a Series Circuit Voltage in a Series Circuit Voltage in a Parallel Circuit Voltage in a Parallel Circuit Resistance through Components Resistance through Components Charge in Circuits Charge in Circuits Energy in Circuits Energy in Circuits Mains Electricity Mains Electricity National Grid National Grid Wiring a Plug Wiring a Plug Fuses and Safety Fuses and Safety Cost of Electricity Cost of Electricity

Circuits Current, Iflow of electrons around the circuit Current, Iflow of electrons around the circuit (Amps)(how fast the electrons travel around) Voltage, VDriving force that pushes electrons Voltage, VDriving force that pushes electrons (Volts)(electrical pressure) Resistance, RSlows down the electrons Resistance, RSlows down the electrons (Ohms)(resists the flow of the electrons) V IR

Current in a Series Circuit The current stays the same everywhere in a series circuit Current here = 5A

Current in a Parallel Circuit Current here = 9A Current splits in 3 ways Current here = 3A The current splits along strands in a parallel circuit

Voltage in a Series Circuit V VV Voltage here = 4V Voltage here = 12V Voltage here = 4V The voltage splits along components in a series circuit

Voltage in a Parallel Circuit The voltage stays the same along strands in a parallel circuit VV Voltage here = 12V

Resistance Through Components I V I V I V 1. Resistor 3. Diode 2. Bulb

Charge in Circuits Electrons travel around a circuit  electricity Electrons travel around a circuit  electricity Each electron carries energy with it Each electron carries energy with it Each electron has a negative charge Each electron has a negative charge In a circuit the total charge, Q, can be calculated by finding how much charge flows in the circuit: In a circuit the total charge, Q, can be calculated by finding how much charge flows in the circuit: Time, t (secs) Q IT

Energy in Circuits Energy, Eflow of energy around the circuit Energy, Eflow of energy around the circuit(Joules) Voltage, VDriving force that pushes electrons Voltage, VDriving force that pushes electrons (Volts)(electrical pressure) Charge, QCharge carried by the electrons Charge, QCharge carried by the electrons(Coulombs) E QV

Mains Electricity The UK mains supply is V The UK mains supply is V Mains electricity is AC (alternating current) Mains electricity is AC (alternating current) The electricity in the mains supply switches direction 50 times per second (but this is too fast to see so lights don’t appear to flicker… although they are, 50 times every second!) The electricity in the mains supply switches direction 50 times per second (but this is too fast to see so lights don’t appear to flicker… although they are, 50 times every second!) The larger the current (faster the electrons travel), the greater the friction produced The larger the current (faster the electrons travel), the greater the friction produced Friction produces heat Friction produces heat This heat is used for kettles, cookers, irons…

National Grid National Grid = Power station  step-up transformer  pylons  step-down transformer  homes Electricity is produced in power stations Electricity is produced in power stations It is transported along pylons at very high voltage (400,000V) It is transported along pylons at very high voltage (400,000V) The higher the voltage, the lower the current… The higher the voltage, the lower the current… and the lower the current the smaller the heat (energy) loss and the lower the current the smaller the heat (energy) loss The high voltage is not safe for domestic use… The high voltage is not safe for domestic use… so the voltage is stepped-down to V so the voltage is stepped-down to V

Wiring a Plug Left bLue (neutral) Right brown (live)

Fuses and Safety Live wire alternates between +ve and –ve voltage Live wire alternates between +ve and –ve voltage Neutral wire is always at 0V Neutral wire is always at 0V Earth wire and fuses are there for safety Earth 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 case 2) big current flows through earth wire… 3) … 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) 2) the circuit breaks  the supply is broken

Cost of Electricity Electricity bills show how many units of electricity you used Electricity bills show how many units of electricity you used 1 unit = 1 kilowatt-hour (an amount of energy) 1 unit = 1 kilowatt-hour (an amount of energy) 1 kilowatt-hour = amount of electrical energy used by a 1kW appliance left on for 1 hour 1 kilowatt-hour = amount of electrical energy used by a 1kW appliance left on for 1 hour Cost = Power x Time x Cost of 1kWh (kW) (hrs) (kW) (hrs) Note: 1kW = 1000W, 1hr = 3600secs Note: 1kW = 1000W, 1hr = 3600secs

Summary Voltage = Current x Resistance Voltage = Current x Resistance Series:current stays the same Series:current stays the same voltage shared between components Parallel:current splits between strands Parallel:current splits between strands voltage stays the same between strands Charge = Current x Time Charge = Current x Time Energy = Charge x Voltage Energy = Charge x Voltage Mains is AC ( V) Mains is AC ( V) High voltage = low heat (energy) loss… but is unsafe High voltage = low heat (energy) loss… but is unsafe Safety features of plugs are: earth wire, fuse Safety features of plugs are: earth wire, fuse Cost of electricity = Power x Time x Cost of 1kWh Cost of electricity = Power x Time x Cost of 1kWh