CIE AS Physics (9702) 2019-2021

Revision Notes

11.1.2 Potential Difference

Defining Potential Difference

  • A cell makes one end of the circuit positive and the other negative. This sets up a potential difference (d) across the circuit
  • The potential difference across a component in a circuit is defined as the energy transferred per unit charge flowing from one point to another
  • The energy transfer is from electrical energy into other forms
  • Potential difference is measured in volts (V). This is the same as a Joule per coulomb (J C-1)
    • If a bulb has a voltage of 3 V, every coulomb of charge passing through the bulb will lose 3 J of energy
  • The potential difference of a power supply connected in series is always shared between all the components in the circuit

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

The potential difference is the voltage across each component in a circuit

 

  • Potential difference or voltage is measured using a voltmeter
  • A voltmeter is always set up in parallel to the component you are measuring the voltage for

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

Potential difference can be measured by connecting a voltmeter in series between two points in a circuit

 

Calculating Potential Difference

  • The potential difference is defined as the energy transferred per unit charge
  • Another measure of energy transfer is work done
  • Therefore, potential difference can also be defined as the work done per unit charge

 

Potential difference equation, downloadable AS & A Level Physics revision notes

Potential difference is the work done per unit charge

 

Worked example

Worked example potential difference, downloadable AS & A Level Physics revision notes

  • Both lamps have the same current, which means charge flows at the same rate in both
  • The 240 V lamp has 20 times more voltage than the 12 V lamp
  • Voltage is the energy transferred (work done) per unit charge
  • This means the energy transferred to each coulomb of charge in the 240 V lamp is 20 times greater than for the 12 V lamp
  • This makes the 240 V lamp shine much brighter than the 12 V lamp

 

Exam Tip

Think of potential difference as being the energy per coulomb of charge transferred between two points in a circuit

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