Energy Transfers Flashcards
Energy transfers & Power P (W)
Rate at which energy is transferred (1W is 1J per second) P = E/t
Power of components: P = VI & P = I^2 x R
Total energy transferred by appliance depends on how long it is on, the power its operating at
Power of appliance is energy it transfers per second. More J transferred in set time - higher power
Power rating - max safe power.
But high power could be less efficient, only transfers same useful amount
Appliances generating thermal energy have higher power rating
Energy Transfers
When a charge flows in circuit, work is done against resistance of circuit - E = QV
Energy transferred = charge flow x p.d
Energy transfers in appliances
Appliances designed to bring about energy transfers
Electrical energy -> kinetic energy (fans), or to thermal energy (kettle) or to both (hair dryer)
Amount of energy transferred by electrical work: E = Pt
Total energy transferred by appliance depends on how long it is on, the power its operating at
National Grid
Electrical power is transferred via a system of cables and transformers linking power stations to consumers
Step-up transformer: less energy lost in power cables when p.d is very high
Step-down transformer: reduces p.d to 230V for domestic use - safer
Efficient as high current in cable -> more energy is dissipated to the surroundings through heat. As high currents waste more energy than low currents, electrical power is transported around the grid at a high voltage and a low current.
