Physics revision p1-p5

TOPIC 1 - ENERGY (P1)- Energy is never used up, instead it is only transfer between stores system = single object. Energy may enter or leave a system.Closed system is a system which matter energy cannot enter or leave.Energy can be transferred by heating up the system - for example water gains energy when is is boiled. Energy is transferred to the thermal energy store.Energy can also be transferred by "doing work"work done = energy transferredWork is done against resistance - The initial force exerted by a person when throwing a ball upwards does work. It causes and energy transfer from the chemical energy store from the persons arms to the genetic energy store go the ball and the arm.

Specific Heat Capacity:Equation E=M*C*CHANGE IN TempE=energy (joules)M=Mass (kg)C= Specific Heat capacity (jog)Definition : Amount of engirt needed to raise the temperature of 1kg of a substance by 1 degreeConsideration of energy and power:P=E/TPower=energy Transferred(j)/Time(s)p-w/tPower=Workdone/timepower = rate of energy transfer power is measured in watts (one watt = one joule of energy transferred per second)conservation of energy principle :Energy can be transferred usefully,stored or dissipated but can never be created or destroyed

Conduction and ConvectionCONDUCTION is the process where vibrating parties transfer energy to neighbouring particlesConduction occurs mainly in solids CONVECTION IS when energetic particles move away from a hot region to a cold region Convection only occurs in Liquids and gasses. Energy is transferred by heating to the thermal store of the liquid or gas.Radiators create convention currents. Energy is transferred from the radiator to near by air particles by conduction. The air by the radiator becomes warmer and less dense. The warm air rises and is replaced by cooler air which is then heated by the radiator. The cycle Repeats causing a flow of air to circulate around the roomto be finished

Alternating current :direct current - current which only flows in one direction Alternating current - current which repeatedly reverses its directions, flows one way than the other. Its frequency is the number of cycles it passes through each second.uk mains frequency is 50 cycles per second / 50hzStep up transformer :Is used to transfer energy from power station to national grid. These transformers are used to make the alternating potential difference much bigger typically from about 25,000 to 132,000Step down transformer :Used to supply electricity from the national grid to the consumers in homes and offices. They are supplied electricity which has the same power as 230V Direct current supply. Factories are supplied with a much larger p.d : from 100kv to 30KvBy making the potential different large, much less current is needed to transfer the same amount of power so the power loss due to the resistance heating in the cables is much reduced.This means that the national grid is an efficient way to transfer powerPlugs and cables:Some appliances have earth wires, such as heaters. When you plug a heater in the plug case may sometimes be metal. The earth wire within th plug is there to stop the plug from becoming live if the live wire was to break and touch the case.Plastic materials are good insulators as they are double insulated, therefore they require no earth wire connection. All appliances sold in the uk with a plastic case must be double insulated.Earth wire - connected to the ground at 0v and only carries current if there is a fault. The longest pin of a 3 pin plug is designed to make contacted with the earth wire if the socket so when you plug an appliance in it is automatically earthed. The metal pins of a plug is made out of brass as brass is a good conductor and does not oxidise or rust. Plug is shapes to that wires and cables cannot touch each other when sealed.to be finished