Power Ks4 Electricity

Aims Work out what Power means Define a Formula P = VI Define Units 1W = 1J/s

Power Delivery When we talk about Power what we mean is “the amount of energy delivered per second” 1 Joule / 1 Second = 1 Watt It then makes sense that the Power used by a component can be found from the product of current through and voltage across the component; Power = Voltage x Current P = V x I

Example In this circuit the Voltmeter = 4V and the Current = 1A Power = Voltage x Current P = V x I P = 4V x 1A P = 4J/C x 1C/s P = 4J/s P = 4W 4V 1A

Analogy Another way of thinking about it is saying that the current carries the energy; 4V 1A CCCC C C CC C 1J C As the Coulombs of Charge move they release their energy as heat and light (through the bulb) C 1J = 1 Coulomb of charge = 1 Joule of energy = 1 Second of time

Analogy 2 If the voltage increases, more energy is delivered so the power increases; 5V 1A CCCC C C CC C 1J C Power = 5V x 1A = 5J/s = 5W 1J C = 1 Coulomb of charge = 1 Joule of energy = 1 Second of time

Analogy 3 If the current increases, more energy is delivered so the power increases; 4V 2A CCCC C C CC C C 1J Power = 4V x 2A = 8J/s = 8W CCCC C C CC C C 1J C = 1 Coulomb of charge = 1 Joule of energy = 1 Second of time

Transmission Lines Ks4 Electricity

Power Loss

Power Use by a PC Ks4 Electricity

PC Energy Use Example Energy = Power x Time Energy = 145W x 1 hour Energy = 145W x 3600s E = 145J/s x 3600s E = J E = 522kJ Here is an example of the energy useage of a home computer. Each internal component transfers a variable amount of energy. If you left this PC on for an hour it would transfer;