Voltage (Cambridge (CIE) IGCSE Co-ordinated Sciences (Double Award)): Revision Note

Voltage

• Voltage is supplied by a source, such as:

  • a cell

  • batteries (multiple cells)

  • an electrical generator

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

• This creates a voltage across the circuit

  • Voltage is also sometimes called potential difference (or p.d.)

• The voltage of the source causes a current to flow in the circuit

Voltage in a series circuit

• In a series circuit, the voltage of the source is shared between the components

• The sum of voltages across the individual components is equal to the total voltage of the power supply

• If the components have equal resistance, then the voltage is shared equally

In a series circuit, the components share the voltage of the power supply

Measuring voltage

• Voltage can be measured using a voltmeter

• Voltmeters must be set up in parallel with the component being measured

  • This is because voltage (or potential difference) is the difference in electrical potential between two points

  • Therefore, a voltmeter has to be connected to two points in the circuit 

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

• Voltmeters can be

  • digital (with an electronic read out)

  • analogue (with a needle and scale)

Analogue voltmeters

• Analogue voltmeters are subject to parallax error

  • Always read the meter from a position directly perpendicular to the scale

• Typical ranges are 0.1-1.0 V and 0-5.0 V for analogue voltmeters although they can vary

  • Always double-check exactly where the marker is before an experiment, if not at zero, you will need to subtract this from all your measurements

  • They should be checked for zero errors before using

Voltmeters can be either analogue (with a scale and needle) or digital (with electronic read-out)

Digital voltmeters

• Digital voltmeters can measure very small voltages, in mV or µV

• Digital displays show the measured values as digits and are more accurate than analogue displays

• They’re easy to use because they give a specific value and are capable of displaying more precise values

  • However digital displays may 'flicker' back and forth between values and a judgement must be made as to which to write down

• Digital voltmeters should be checked for zero error

  • Make sure the reading is zero before starting an experiment, or subtract the “zero” value from the end results