There are 3 different key terms that will appear a lot throughout this whole electricity section. These are current, potential difference and resistance. Here is a brief description of these 3 terms:

The current (I) through a component depends on both the resistance of the component (R) and the potential difference across the component (V). The equation and formula triangle that links potential difference, current and resistance is shown below.

- Current is the flow of electrical charge around a circuit per second; the greater the flow of electrical charge per second, the greater the current. We measure current in ampere (A).
- Potential difference is the driving force that pushes the electrical charge (current) around a circuit. The source of potential difference is usually a battery or cell. Potential difference is measured in volts (V) and is sometimes referred to as voltage.
- Resistance opposes the flow of electrical charge (current) in a circuit. Resistance converts electrical energy into thermal energy. Resistance is measured in ohms (Ω)

The current (I) through a component depends on both the resistance of the component (R) and the potential difference across the component (V). The equation and formula triangle that links potential difference, current and resistance is shown below.

We can work out the current through a component by dividing the potential difference by the resistance.

Let’s now have a few maths examples

**Example 1**

A 6 Ω resistor has a potential difference across it of 12 V. Find the current.

We find the current (I) passing through the resistor by dividing the potential difference (V) by the resistance (R).

The question tells us that the potential difference is 12 V and the resistance is 6 Ω. We sub these values into the equation.

The current through the resistor is 2 A.

**Example 2**

The resistance of a component is 5 Ω and the current through the component is 3 A. Find the potential difference across the component.

We find the potential difference across a component by multiplying the current by the resistance.

The question tells us that the current is 3 A and the resistance is 5 Ω. We sub these values into the calculation.

The potential difference across the component is 15 V.

**Calculating These Values**

Let’s suppose that we have the circuit below with a filament bulb.

We measure the current through a component (or around a circuit) by using an ammeter. We can place this ammeter anywhere on the main circuit, but never in parallel with the component; we place the ammeter in series with whatever we are testing.

We measure the potential difference across a component by using a voltmeter. We place the voltmeter in parallel around the component that we are finding the potential difference for; in the circuit above, we place the voltmeter in parallel around the filament bulb.

I have added the ammeter and voltmeter with some values to the circuit.

We measure the potential difference across a component by using a voltmeter. We place the voltmeter in parallel around the component that we are finding the potential difference for; in the circuit above, we place the voltmeter in parallel around the filament bulb.

I have added the ammeter and voltmeter with some values to the circuit.

For the above circuit, the ammeter reads 4 A and the voltmeter reads 10 V. We can find the resistance of the filament bulb from these values by dividing the potential difference (10 V) by the current (4 A).

The resistance of the filament bulb is 2.5 Ω.