Voltage & Energy (Edexcel IGCSE Physics)

Revision Note

Ashika

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Ashika

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Voltage

  • 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

voltage-in-a-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

Voltmeter in a circuit, downloadable AS & A Level Physics revision notes

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

Examiner Tips and Tricks

When you are building a circuit in class, always connect the voltmeter last. Make the whole circuit first and check it works, and then connect the voltmeter so that the leads are on each side of the component you are measuring. This will save you a lot of time waiting for your teacher to troubleshoot your circuit!

You might sometimes see voltage called potential difference. This term can be useful when thinking about voltmeters as the potential difference describes a difference between two points, therefore the voltmeter has to be connected between two points in the circuit.

Calculating voltage

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

energy transferred = charge × voltage

E space equals space Q space cross times space V

  • 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

Energy Charge Voltage Formula Triangle, downloadable IGCSE & GCSE Physics revision notes

Formula triangle for the energy transferred, voltage and charge equation

Worked Example

The normal operating voltage for a lamp is 6 V.

Calculate how much energy is transferred in the lamp when 4200 C of charge flows through it.

Answer:

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 space equals space Q space cross times space V

Step 3: Substitute the known values and calculate the energy transferred

E = 6 × 4200 = 25 200 J

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

Examiner Tips and Tricks

Don't be confused by the symbol for voltage (the symbol V) being the same as its unit (the volt, V). Learn the equation and remember especially that one volt is equivalent to 'a joule per coulomb'.

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Ashika

Author: Ashika

Expertise: Physics Project Lead

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.