Voltage & Energy (Edexcel IGCSE Physics)

• Voltage is defined as

The energy transferred per unit charge passing between two points

• Voltage is measured in units of volts (V)
  • 1 volt is equivalent to the transfer of 1 joule of energy by 1 coulomb of charge, or 1 V = 1 J/C

• The terminals of a cell make one end of the circuit positive and the other negative

• As electrons flow through a cell, they gain energy
  • For example, in a 12 V cell, every coulomb of charge passing through gains 12 J of energy

• As electrons flow through a circuit, they lose energy
  • For example, after leaving the 12 V cell, each coulomb of charge will transfer 12 J of energy to the wires and components in the circuit

Electrons gain energy as they pass through a cell. As they flow through the light bulb, energy is transferred to the surroundings by heating and radiation

Measuring voltage

• Voltage can be measured using a voltmeter
• Voltmeters must be set up in parallel with the component being measured

Voltage can be measured by connecting a voltmeter in parallel between two points in a circuit

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

energy transferred = charge × voltage

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

• This can be rearranged using the formula triangle below:

Energy charge voltage formula triangle

Formula triangle for the energy transferred, voltage and charge equation

• Check out this revision note on speed, distance and time if you need a reminder on how to use formula triangles