physics - resistance

formula linking resistance, current and PD

PD = Current x resistance

current changing effect in ohmic conductors

the resistance of ohmic conductors doesn’t change with current. this is because they don’t heat up

current changing effect in lamp

when current flows through a lamp, it transfers heat to the thermal energy store

resistance increases with temperature, so as the current increases, the lamp heats up, and so the resistance increases

resistance relies on…

temperature

resistance

slows the current down

resistance practical

1 battery, one ammeter in series, one voltmeter in parallel, a test wire on top of a ruler

change the length of the wire 10cm at a time, noting down the current and pd across the circuit for each length

do pd/current to get resistance for each length