**Circuit Symbols**

**Potential difference, current & resistance**

**Potential difference (V)** is the amount of joules per coulomb of charge, it is measured in volts (V).

**Current (I)** is the amount of charge per second passing a point in a circuit, it is measured in amps (A).

**Resistance (W)** ratio of potential difference across a component to the current flowing through it, it is measure in ohms (W).

**A resistor at constant temperature (ohmic conductor)**

Current is directly proportional to potential difference. Doubling the potential difference doubles the current in the circuit. The resistance remains the same. Plotting a graph of potential difference against current gives a straight line passing through the origin (0,0).

**Ohm’s Law**

“The electrical current in a conductor is proportional to the potential difference applied to it provided the temperature remains the same.”

Potential difference = current x resistance

(V, volts V) (I, amps A) (R, ohms W)

**Measuring current and potential difference**

Current is measure with an ammeter, ammeters are always connected in series.

Potential differences are measured using a voltmeter, voltmeters are connected in parallel.

By measuring the current and potential difference you can calculate the resistance.