Potential Difference (Edexcel GCSE Physics: Combined Science)

• The terminals of a cell make one end of the circuit positive and the other negative
• This sets up a potential difference across the circuit
  • This is sometimes known as the voltage

• Potential difference is defined as:

The amount of energy transferred per unit of charge passing through the terminals

• This means that one volt (the unit of potential difference) is equivalent to one joule (the unit of energy) per coulomb (the unit of charge):

1 V = 1 J / C

• Potential difference can be calculated using the equation below:

• Where:
  • V = potential difference, measured in volts (V)
  • E = energy transferred, measured in joules (J)
  • Q = charge moved, measured in coulombs (C)

• The equation for potential difference can be rearranged using the formula triangle below:

Energy, charge, potential difference formula triangle

• Potential difference (or voltage) is measured using a voltmeter
• A voltmeter is always set up in parallel to the component being measured
  • This is described as measuring voltage 'across' the component

Potential difference (voltage) can be measured by connecting a voltmeter in parallel between two points in a circuit. Here, the voltmeter is measuring the voltage across the resistor

Step 1: List the known quantities

• • Voltage (potential difference), V = 6 V
  • Charge moved, Q = 4200 C

Step 2: State the equation linking potential difference, energy and charge

• • The equation linking potential difference, energy and charge is:

Step 3: Rearrange the equation for energy transferred

• • Using the formula triangle, the energy transferred is given by:

E = V × Q

Step 4: Substitute the known values and calculate the energy transferred

E = 6 × 4200

E = 25 200 J

• • Therefore, 25 200 J of energy is transferred in the lamp