In part 1 we talked about the resistance of a component.

The resistance of a component is the ratio of the p.d. (voltage) across it to the current flowing through it. Materials with zero resistance are called superconductors. Resistance is measured in ohms (Ω)

Resistance = P.d. ÷ Current

R = V/I

If we re-arrange this, we get

Current = P.d. ÷ Resistance

I = V/R

If the resistance doesn’t change, then we can say the current through a component is directly proportional to the P.d. across it.

This leads us to Ohm’s Law: The current through a component is directly proportional to the p.d. across it for constant physical conditions.

The physical variable that has the greatest effect on resistance is temperature. Generally speaking, if the temperature remains constant, we can say the resistance of a passive component remains constant.