# 11.1.2 Potential Difference

### Defining Potential Difference

• A cell makes one end of the circuit positive and the other negative. This sets up a potential difference (d) across the circuit
• The potential difference across a component in a circuit is defined as the energy transferred per unit charge flowing from one point to another
• The energy transfer is from electrical energy into other forms
• Potential difference is measured in volts (V). This is the same as a Joule per coulomb (J C-1)
• If a bulb has a voltage of 3 V, every coulomb of charge passing through the bulb will lose 3 J of energy
• The potential difference of a power supply connected in series is always shared between all the components in the circuit

The potential difference is the voltage across each component in a circuit

• Potential difference or voltage is measured using a voltmeter
• A voltmeter is always set up in parallel to the component you are measuring the voltage for

Potential difference can be measured by connecting a voltmeter in series between two points in a circuit

### Calculating Potential Difference

• The potential difference is defined as the energy transferred per unit charge
• Another measure of energy transfer is work done
• Therefore, potential difference can also be defined as the work done per unit charge

Potential difference is the work done per unit charge

#### Worked example

• Both lamps have the same current, which means charge flows at the same rate in both
• The 240 V lamp has 20 times more voltage than the 12 V lamp
• Voltage is the energy transferred (work done) per unit charge
• This means the energy transferred to each coulomb of charge in the 240 V lamp is 20 times greater than for the 12 V lamp
• This makes the 240 V lamp shine much brighter than the 12 V lamp

#### Exam Tip

Think of potential difference as being the energy per coulomb of charge transferred between two points in a circuit

### Author: Ashika

Ashika graduated with a first-class Physics degree from Manchester University and, having worked as a software engineer, focused on Physics education, creating engaging content to help students across all levels. Now an experienced GCSE and A Level Physics and Maths tutor, Ashika helps to grow and improve our Physics resources.
Close