Transfer of Thermal Energy (Cambridge O Level Physics)

A student is investigating ways of slowing the rate of cooling of hot liquids in a container.
The student knows that a lid will reduce the rate of cooling. He wants to find out if the thickness of the lid makes any difference to the rate of cooling.

 
Plan an experiment which will enable him to compare the effects of lids of different thicknesses.

In your plan, you should:

• list the apparatus needed
• explain briefly how you would carry out the investigation, including the measurements to be taken
• state any key variables that would need to be kept the same
• draw a suitable table or tables, with column headings, to show how the readings would be displayed (you are not required to enter any readings in the table)
• explain how you would use your readings to reach a conclusion.

You may draw a diagram if it helps to explain your plan.

Students are investigating the cooling of hot water in a beaker.

They are using the apparatus shown in Fig. 2.1.

Record room temperature θ_R shown on the thermometer in Fig. 2.1.

θ_R = ........................................................ 

A volume of 150 cm³ of hot water is poured into the beaker and the initial temperature θ is recorded in Table 2.1.

The temperature of the water is recorded every 30 s. The values are shown in Table 2.1.

(i)

Complete the headings in Table 2.1.

[1]

(i)

Describe one precaution that you would take to ensure that the temperature readings in the experiment are as accurate as possible.

[1]

Students are investigating how the use of a lid or insulation affects the rate of cooling of hot water in a beaker. They use the apparatus shown in Fig. 2.1.

Record the room temperature θ_R shown on the thermometer in Fig. 2.1.

• 100 cm³ of hot water is poured into beaker A and the initial temperature θ is recorded in Table 2.1.
• The temperature θ of the water at times t = 30 s, 60 s, 90 s, 120 s, 150 s and 180 s are shown in Table 2.1.
• This process is repeated for beaker B.

Complete the headings and the time column in Table 2.1.

Table 2.1

Write a conclusion stating whether the insulation or the lid is more effective in reducing the cooling rate of the water in the beakers in this experiment.

Justify your answer by reference to the results.

One student thinks that the experiment does not show how effective insulation is on its own or how effective a lid is on its own.

 
Suggest an additional experiment which could be used to show how effective a lid or insulation is.

 
Explain how the additional results could be used.

where T = 180 s and θ₀ and θ₁₈₀ are the temperatures at time t = 0 and time t = 180 s.
Include the unit for the cooling rate.

x_A = ........................................................ [2]

A student investigates the effect of the colour of the surface of a metal container on the rate of loss of heat from the container. She knows that black surfaces are better radiators of thermal energy than white surfaces and wants to investigate the effect of other colours.

The following apparatus is available:

metal containers each with the outer surface painted a different colour

a thermometer

a stop-watch

a supply of hot water.

She can also use other apparatus and materials that are usually available in a school laboratory.

Plan an experiment to investigate the effect of the colour of the surface of a metal container on the rate of loss of heat from the container.

You should:

• draw a diagram of the apparatus used
• explain briefly how you would carry out the investigation
• state the key variables to be kept constant
• draw a table, or tables, with column headings, to show how you would display your readings (you are not required to enter any readings in the table)
• explain how you would use your readings to reach a conclusion.

Some students are investigating how the volume of water affects the rate at which water in a beaker cools.

They are using the apparatus shown in Fig. 2.1. 

Describe one precaution which should be taken to ensure that the temperature readings in the experiment are as accurate as possible.

Write a conclusion stating how the volume of water in the beaker affects the rate of cooling of the water. Justify your answer by reference to the results.

A student suggests that it is important that the experiments with the two volumes of water should have the same starting temperatures.

State whether your values for x₁ and x₂ support this suggestion. Justify your statement with reference to your results.

Another student plans to investigate whether more thermal energy is lost from the water surface than from the sides of the beakers.

Describe an experiment that could be done to investigate this.

You may draw a diagram to help your description.