electricity

• flow of electrons or electrical charge in a circuit is electric current
• when electrons return to the positive end of the cell they are carrying less energy then when they left the negative end of the cell
• conventional current - goes from positive to negative
• series circuits go in one direction and have no branches
• current is measured in amps with an ammeter
• in a series circuit current is the same all the way around
• parallel circuits contain branches
• the current in the branches adds up to the total current leaving the cell
• potential difference of 1 V tells us that one joule of energy is transferred per coulomb of charge that is moving through the circuit
• all electrical energy is transferred to the other forms of energy ( eg light or thermal )
• total energy transferred by current is shared between components
• for components connected in parallel the potential difference across each component is the same
• the cells in a battery must point in the same direction or it cancells out the potential difference
• charge is measured in coulombs (C)
• the current is the rate of the flow of charge
• charge = current x time
• energy transferred = charge flow x potential difference
• the cell contains chemical energy which is transferred to electric energy carried by the current
• resistance tells us the amount of voltage needed to drive a current
• high potential difference = high resistance
• resistance is measured in ohms
• voltage = current x resistance
• resistors reduce the P.D of components and the electrical energy
• current moving through a resistor is directly proportional to P.D.
• ohmic resistor = resistance does not change when current increases
• resistance is only constant if temperature is constant
• when a filament lamps temperature increases the resistance increases
• at high temperatures the atoms vibrate more which causes more resistance and the need for a higher potential difference
• current in a diode only flows in one direction
• diodes have a very high resistance in the reverse direction
• diodes control the flow of current in circuits
• LED gives off light when current flows through
• V = I x R
• resistors in series add together
• the total resistance of two resistors in parallel is less than the resistance of the smallest individual resistor
• in dark conditions LDR has a very high resistance
• the resistance of a thermistor decreases if the temperature increases ( the colder it is the more resistance there is )
• household appliances transfer electrical energy into thermal or kinetic energy
• power is the rate energy is transfered
• appliances that generate thermal energy have a higher power rating