The relationship between voltage, current and resistance is defined by Ohm's Law.
- The potential of a battery is measured in volts (V).
- The flow of current in a circuit (I) is measured in amperes.
- The power rating of a consumer is measured in watts (W).
- The resistance (R) of a circuit is measured in Ohms.
Ohm's law, for practical work can be described as -
Power is calculated by multiplying Volts x Amps -
By transposing either of these formulae, the value of any unit can be calculated if the other two values are known.
For example, if a battery of 12 V is connected to a bulb of 60 W:
the current flowing in the circuit can be calculated by using -
the bulb resistance can be calculated by using -
To use either of the following triangles, put your finger over the value you want to find. Multiply the remaining values if side by side, or divide if one is over the other.