energy transfers Flashcards
2 equations for power of a circuit
P = IV
P = I^2R
power (watts) = current (amperes) x pd (volts)
power = current^2 x resistance
equation of energy transferred power and time
E = Pt
energy (joules) = power (watts) x time (secs)
link an equation linking energy transferred charge flow and pd
E = QV
energy (joules) = charge (coulombs) x pd (volts)
2 main factors amount of energy transferred by an appliance depend on
- how long used for
- power
describe energy transferred in a battery powered torch
- battery converts chemical energy to electrical energy
- bulb converts electrical energy into light as well as waste energy in the form of heating
describe energy transfers in a battery powered motor
- battery converts chemical energy to electrical energy
- motor converts electrical energy into kinetic energy as well as waste energy in form of heating due to friction
3 things determine power of circuit device
- pd across circuit
- current through circuit
- amount of energy transferred in a given time
purpose of national grid
link power stations to consumers so they have access to a source of electricity
2 types of transformers used in national grid
- step-up transformers
- step-down transformers
where are step-up transformers found in the national grid and what do they do
- used when connecting power stations to transmission cables
- increase pd
where are step-down transformers found in the national grid and what do they do
- used in connecting transmission cables to domestic buildings like houses
- decrease pd
why do transmission lines transfer electricity at high potentials
- result in low current
- lower the current the less energy wasted as heat
- more efficient
why does potential need to be decreased between transmission lines and houses
- lower potentials are safer for domestic use and reduced the likelihood of severe electrocution
- appliances designed for 230V
