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Electric Kettle

Age 14 to 16 Challenge Level:


The diagram shows a simple circuit: the cell provides energy, V volts, which causes a current, I amps, to flow around the circuit. There is also a resistance, R ohms.
 circuit diagram
This circuit provides a simple model for what happens in an electric kettle: a resistance converts electrical energy into heat energy by impeding the flow of electrons around the circuit.

The table shows data collected from a circuit like this.


Resistance (ohms) Temperature (degrees Celsius)
5 44.9
6 50
7 55.1
8 59.9
9 65
10 70.1



  • Draw a graph of this data, with the resistance on the horizontal axis, putting a straight line through the points.
  • Find the gradient of the line.
  • Find the equation of the line.





Once you have found the equation, discuss these questions:



  • What resistance would you need to heat water to 100 C°?
  • What would the temperature be if the resistance was zero?
  • Do you think that in practice, any circuit can have zero resistance?