CURRENT ELECTRICITY Relationship between current and potential difference.

RESISTANCE
Different conductors resist currant flow by different amounts under different conditions, this property is called its resistance R,

R = ^V /I where V is the potential difference and I is the current. The unit of resistance is the Ohm ( Ω ), which is defined as the resistance of a conductor such that when a p.d. of 1 volt is applied across it induces a currant of 1 Amp.

OHM'S LAW
Ohm's law states that

the current through an ohmic conductor is directly proportional to applied P.D, given that there are no changes in the physical conditions of the conductor.

i.e that the resistance R is constant.

EXPERIMENTAL MEASUREMENT
The circuit opposite is used to test the relationship between I and V for different things placed in for T. After an adjustment has been made on the variable resistor time is given for the material to reach equilibrium. If the test is at a constant temeperature a temperature controled water bath is used to keep the material undertest at a constant temperature.

Rob Coles 27 May 1996 12:31:04