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AQA · GCSE · Combined Science · Higher

Non-linear kettle heating results

Q05.4 1 mark

Figure 5 shows how the mass of water in the kettle affected the time taken for the kettle to switch off.

Line graph titled Figure 5. The x-axis is mass of water in grams from 0 to 1200. The y-axis is time taken for the kettle to switch off in seconds from 0 to 200. The curve starts above the origin at about 10 seconds when mass is 0 g, then rises non-linearly to about 138 seconds at 1000 g.

Figure 5

Enlarged question image

Line graph titled Figure 5. The x-axis is mass of water in grams from 0 to 1200. The y-axis is time taken for the kettle to switch off in seconds from 0 to 200. The curve starts above the origin at about 10 seconds when mass is 0 g, then rises non-linearly to about 138 seconds at 1000 g.
Figure 5

Suggest why the results give a non-linear pattern.

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Marking points

  1. 1 State that as the mass of water increases, the rate of energy transfer to the surroundings per kg of water decreases.
  2. 2 Or state that as the mass of water increases, the kettle becomes more efficient.

Full-mark answer

As the mass of water increases, less energy is transferred to the surroundings per kg of water, so the time does not increase in direct proportion to the mass.

Why this answer loses marks

Because the graph curves.

This describes the pattern but does not give a physical reason for it.

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