Voltage & Energy (Edexcel IGCSE Physics)

• 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

• The equation linking the energy transferred, voltage and charge is given below:

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

• This can be rearranged using the formula triangle below:

Step 1: List the known quantities

• • Voltage, V = 6 V
  • Charge, Q = 4200 C

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

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

E = V × Q

Step 3: 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

• Potential difference is measured using a voltmeter, which can be either
• • Digital (with an electronic read out)
  • Analogue (with a needle and scale)
• Voltmeters are connected in parallel with the component being tested
  • The potential difference is the difference in electrical potential between two points, therefore the voltmeter has to be connected to two points in the circuit 

Voltmeters are connected in parallel to the component being tested