Topic Menu

Cyber-chess a chess instruction site

Heat Questions - GCSE Level

Q15. A householder monitored how the air temperature inside his house changed over a two hour period. The householder measured the temperature every 15 minutes.

The graph shows how the temperature changed with time.

(a)

(i) The householder used a digital thermometer to measure the temperature. Which of the following intervals would be an appropriate resolution for the digital thermometer?

0.5 °C
1 °C
5 °C

0.5 °C

[1 mark]

(ii) The householder's results are shown above on a line graph. Why would it not be appropriate to use the results to plot a bar chart?

The data is continuous or both variables are continuous or independent variable is continuous or time is continuous.

[1 mark]

(b) The householder's heating is controlled by a thermostat. The thermostat switches the heating on when the temperature decreases below a certain temperature.

(i) At what temperature does the thermostat switch the heating on?

20.5 °C (See graph)

[1 mark]

(ii) Use the graph to determine the number of minutes that the householder's heating was switched on between 07:00 and 09:00.

60 minutes (See graph)

[1 mark]

(c) The householder read the following extract from a newspaper article about reducing energy use in the home:

 

On Monday, the householder set his thermostat at 20.0 °C and recorded the energy, in kWh, used to heat his house.

On Tuesday, the householder set his thermostat at 19.0 °C and recorded the energy, in kWh, used to heat his house.

The table below shows the results of the householder's investigation:

Thermostat setting in °C
Energy in kWh
20.0
8.0
19.0
7.2

(i) The outside temperature was the same on both days.

Give one reason why this was important.

So a fair comparison can be made of the temperature changes or because the outside temperature is a control variable

If you say 'to make it a fair test' you get no marks - even though this is true! Examiners avoid giving marks for saying fair test becasue so many students just say that without knowing why that is the case - so NEVER say that as an answer!

[1 mark]

(ii) Explain how the results shown in the table support the extract from the newspaper article.

Justify your answer with a calculation.

Cost = the number of kWh x the cost per kWh

Saving = 8.0 - 7.2 = 0.8 kWh

0.8 / 8.0 = 0.1 or 10% savings

[2 marks]

(iii) The statement in the extract is not valid for all situations. Suggest why.

Heating can be on for more / less time (than anticipated) because some days it is cooler / warmer (than anticipated)

Just saying temperature (inside / outside) is always changing was considered insufficient to get you the mark - you needed to relate the temperature changes to the time the heating would switch on.

[2 marks]

(9 marks total)