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Electricity

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

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Electricity

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  1. Electricity

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

  3. Circuits • Current, I flow of electrons around the circuit (Amps) (how fast the electrons travel around) • Voltage, V Driving force that pushes electrons (Volts) (electrical pressure) • Resistance, R Slows down the electrons (Ohms) (resists the flow of the electrons) V I R

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

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

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

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

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

  9. Charge in Circuits • Electrons travel around a circuit  electricity • Each electron carries energy with it • 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: Time, t (secs) Q I T

  10. Energy in Circuits • Energy, E flow of energy around the circuit (Joules) • Voltage, V Driving force that pushes electrons (Volts) (electrical pressure) • Charge, Q Charge carried by the electrons (Coulombs) E Q V

  11. Mains Electricity • The UK mains supply is 230-240V • 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 larger the current (faster the electrons travel), the greater the friction produced • Friction produces heat This heat is used for kettles, cookers, irons…

  12. National Grid National Grid = Power station  step-up transformer  pylons  step-down transformer  homes • Electricity is produced in power stations • It is transported along pylons at very high voltage (400,000V) • The higher the voltage, the lower the current… • and the lower the current the smaller the heat (energy) loss • The high voltage is not safe for domestic use… • so the voltage is stepped-down to 230-240V

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

  14. Fuses and Safety • Live wire alternates between +ve and –ve voltage • Neutral wire is always at 0V • Earth wire and fuses are there for safety • 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): 1) surge in current melts the fuses (a thin wire) 2) the circuit breaks  the supply is broken

  15. Cost of Electricity • Electricity bills show how many units of electricity you used • 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 Cost = Power x Time x Cost of 1kWh (kW) (hrs) • Note: 1kW = 1000W, 1hr = 3600secs

  16. Summary • Voltage = Current x Resistance • Series: current stays the same voltage shared between components • Parallel: current splits between strands voltage stays the same between strands • Charge = Current x Time • Energy = Charge x Voltage • Mains is AC (230-240V) • High voltage = low heat (energy) loss… but is unsafe • Safety features of plugs are: earth wire, fuse • Cost of electricity = Power x Time x Cost of 1kWh

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