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AQA · GCSE · Combined Science · Higher

Explaining a non-zero graph intercept

Q05.3 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 line on Figure 5 does not go through the origin.

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Marking points

  1. 1 Say that the heating element or kettle itself took time to heat up before heating the water sufficiently.

Full-mark answer

The kettle or heating element took time to heat up before it could heat the water, so the time was not zero even when extrapolated to zero mass of water.

Why this answer loses marks

Because the graph was drawn incorrectly.

The mark scheme credits the physical reason that the kettle or heating element takes time to heat up, not a generic graph-drawing comment.

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