Energy transfers

A student investigates how the thickness of insulation around a brass cylinder affects how quickly it cools down.

She wraps four identical brass cylinders in different numbers of layers of aerogel sheets.

This is the student's plan:

I will wrap four identical cylinders with 2 layers, 4 layers, 6 layers, and 8 layers of aerogel sheet.
I will heat each brass cylinder in a hot water bath to a high temperature.
I will remove them from the bath, insert a temperature probe into each cylinder, and record the initial temperature.
After 15 minutes, I will measure the temperatures again.

State the independent variable in this investigation.

[1]

State one variable (other than the material or mass of the cylinder) that the student plans to control.

[1]

Explain why it is important to control this variable.

[2]

Suggest a safety precaution for this investigation.

[1]

Complete the table by calculating each missing temperature difference:

Number of layers of aerogel	Starting temperature in $∘C^{\circ}\text{C}$	Temperature after 15 minutes in $∘C^{\circ}\text{C}$
2	92	58
4	89	63
6	95	74
8	91	76

[1]

The student wants to display the data on a graph. Give suitable labels for the axes of her graph.

[3]

The student realizes that it was a mistake to have different starting temperatures. Suggest how she could modify her method to correct this mistake.

[2]