2. Static Electricity 05/06/09 Static electricity is when charge “builds up” on an object and then stays “static”. How the charge builds up depends on what materials are used: + + - - - + + + - - + + + - - - + - + -
5. Electric Current 05/06/09 Electric current is a flow of negatively charged particles (i.e. electrons). By definition, current is “the rate of flow of charge” Note that electrons go from negative to positive - + e - e -
6. More basic ideas… 05/06/09 If a battery is added the current will ________ because there is a greater _____ on the electrons If a bulb is added the current will _______ because there is greater ________ in the circuit
7. Current in a series circuit 05/06/09 In other words, the current in a series circuit is THE SAME at any point If the current here is 2 amps… The current here will be… The current here will be… And the current here will be…
8. Current in a parallel circuit 05/06/09 A PARALLEL circuit is one where the current has a “choice of routes” Here comes the current… And the rest will go down here… Half of the current will go down here (assuming the bulbs are the same)…
9. Current in a parallel circuit 05/06/09 If the current here is 6 amps The current here will be… The current here will be… The current here will be… And the current here will be…
11. Voltage in a series circuit 05/06/09 2V V V V If the voltage across the battery is 6V… … and these bulbs are all identical… … what will the voltage across each bulb be?
12. Voltage in a series circuit 05/06/09 4V V V If the voltage across the battery is 6V… … what will the voltage across two bulbs be?
13. Voltage in a parallel circuit 05/06/09 4V 4V If the voltage across the batteries is 4V… What is the voltage here? And here? V V
14. Summary 05/06/09 In a SERIES circuit: Current is THE SAME at any point Voltage SPLITS UP over each component In a PARALLEL circuit: Current SPLITS UP down each “strand” Voltage is THE SAME across each”strand”
17. Resistance 05/06/09 The resistance of a component can be calculated using Ohm’s Law: Georg Simon Ohm 1789-1854 Resistance is anything that will RESIST a current. It is measured in Ohms, a unit named after me. Resistance = Voltage (in V) (in ) Current (in A) V R I
23. Power and fuses 05/06/09 Power is “the rate of doing work”. The amount of power being used in an electrical circuit is given by: Power = voltage x current in W in V in A Using this equation we can work out the fuse rating for any appliance. For example, a 3kW (3000W) fire plugged into a 240V supply would need a current of _______ A, so a _______ amp fuse would be used (fuse values are usually 3, 5 or 13A). P I V
24. Power and fuses 05/06/09 Copy and complete the following table: Appliance Power rating (W) Voltage (V) Current needed (A) Fuse needed (3, 5 or 13A) Toaster 960 240 Fire 2000 240 Hairdryer 300 240 Hoover 1000 240 Computer 100 240 Stereo 80 240
25. Energy and Power 05/06/09 The POWER RATING of an appliance is simply how much energy it uses every second. In other words, 1 Watt = 1 Joule per second E = Energy (in joules) P = Power (in watts) T = Time (in seconds) E T P
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27. The Cost of Electricity 05/06/09 Electricity is measured in units called “kilowatt hours” (kWh). For example… A 3kW fire left on for 1 hour uses 3kWh of energy A 1kW toaster left on for 2 hours uses 2kWh A 0.5kW hoover left on for 4 hours uses __kWh A 200W TV left on for 5 hours uses __kWh A 2kW kettle left on for 15 minutes uses __kWh
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29. Efficiency 05/06/09 Efficiency is a measure of how much USEFUL energy you get out of an object from the energy you put INTO it. For example, consider a TV: Electrical Energy (200J) Light (80J) Sound (40J) Heat (?) Efficiency = Useful energy out Energy in x100%
