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Ohm's Law

<^< Resistance | Course Index | Worksheet: Ohm's Law >^>

Provided that temperature does not vary, the ratio of p.d. across the ends of a conductor to the current flowing in the conductor is a constant. This relationship is known as Ohm's law and it leads to the formula:

V/I = a constant = R

where V is the potential difference (or voltage drop) in volts (V), I is the current in amps (A), and R is the resistance in ohms (Ω).

The formula may be arranged to make V, I or R the subject, as follows:

V = IxR or I = V/R and R = V/I

It is important to note that when performing calculations of currents, voltages and resistances in practical circuits it is seldom necessary to work with an accuracy of better than ±1% simply because component tolerances are invariably somewhat greater than this. Furthermore, in calculations involving Ohm's Law, it is sometimes convenient to work in units of kΩ and mA (or MΩ and µA) in which case potential differences will be expressed directly in V.

<^< Resistance | Course index | Worksheet: Ohm's Law >^>