Transfer of Thermal Energy (Cambridge (CIE) IGCSE Physics): Exam Questions

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 in °C 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]

Table 2.1

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

[1]

(i) Calculate the average cooling rate x₁ during the first 90s of the experiment. Use the readings from Table 2.1 and the equation

where T = 90 s and θ₀ and θ₉₀ are the temperatures at t = 0 and t = 90 s.

Include the unit for the cooling rate.

 x₁ = ........................................................ [1]

(ii) Calculate the average cooling rate x₂ during the middle 90 s of the experiment. Use the readings from Table 2.1 and the equation

 where T = 90 s and θ₉₀ and θ₁₈₀ are the temperatures at t = 90 and t = 180 s.

x₂ = ........................................................ [1]

(iii) Calculate the average cooling rate x₃ during the last 90 s of the experiment. Use the readings from Table 2.1 and the equation

where T = 90 s and θ₁₈₀ and θ₂₇₀ are the temperatures at t = 180 and t = 270 s.

 x₃ = ........................................................ [1]

(i) The temperature of the water falls as time passes. Use the results from (c) to describe the pattern of the rate of cooling of the water during the experiment.

Justify your answer by reference to the results.

[1]

(ii) Give an estimate of the probable final temperature θ_F of the water if left to cool for many hours.

θ_F = ........................................................ [1]

(i) A student in another school carries out a similar experiment.

She starts with the hot water at a lower initial temperature.

Suggest how her cooling rates are likely to compare with those calculated in (c).

Use the results to explain your answer.

[2]

(ii) State one variable, other than the initial temperature, which the student should control.

[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 in °C shown on the thermometer in Fig. 2.1.

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

• 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.

(i) Calculate x_A, the average cooling rate for beaker A over the whole experiment. Use the readings for beaker A from Table 2.1 and the equation

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]

(ii) Students in another school are carrying out this experiment using identical equipment.

 State why they should make the initial temperature of the water the same as in this experiment if they are to obtain average cooling rates that are the same as in Table 2.1. Assume that the room temperature is the same in each case.

Use the results from beaker A to explain why this factor should be controlled.

[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. 

(i) 200 cm³ of hot water is poured into beaker A and the initial temperature rises to the value shown on thermometer A in Fig. 2.1.

 In the first row of Table 2.1, record this temperature θ_A for time t = 0.

 100 cm³ of hot water is poured into beaker B. The temperature rises to the value shown on thermometer B in Fig. 2.1.

 In the first row of the table, record this temperature θ_B for time t = 0.

[1]

(ii) The temperatures θ_A and θ_B of the water in each experiment at times t = 30 s, 60 s, 90 s, 120 s, 150 s and 180 s are shown in the table.

Complete the headings and the time column in the table.

[2]

Table 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.

(i) Using the results for 100 cm³ of water, calculate the average rate of cooling x₁ for the first 90 s of the experiment. Use the readings from the table and the equation

 where t = 90 s and θ₀ and θ₉₀ are the temperatures at time 0 and at time 90 s. Include the unit for the rate of cooling.

x₁ = ...........................................................[1]

(ii) Using the results for 100 cm³ of water, calculate the average rate of cooling x₂ in the last 90 s of the experiment. Use the readings from the table and the equation

where t = 90 s and θ₉₀ and θ₁₈₀ are the temperatures at time 90 s and at time 180 s. Include the unit for the rate of cooling.

x₂ = ............................................................[1]

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.

A student investigates how partly covering the top of a beaker of water affects the rate at which the water cools. 

The apparatus used is shown in Fig. 1.1.

Read and record the room temperature θ_R, shown on the thermometer in Fig. 1.2. 

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

The student pours 100 cm³ of hot water into a beaker. She places lid A on the beaker. This leaves half of the top of the beaker uncovered, as shown in Fig. 1.3.

She records the temperature of the water in the beaker and immediately starts a stopwatch. She records the temperature θ of the water every 30 s. Her readings are shown in Table 1.1. 

She repeats the procedure using lid B. This leaves a quarter of the top of the beaker uncovered, as shown in Fig. 1.4.

Complete the headings row in Table 1.1. 

Complete the time t column in Table 1.1.

Table 1.1

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

Extended Tier Only

(i)  Write a conclusion to this experiment, stating for which lid the rate of cooling is greater. Justify your answer with reference to the results. 

[2]

(ii) Suggest a change to the apparatus that produces a greater difference between the rates of cooling for lid A and lid B. Explain why the change produces a greater difference. 

 [2]

 Another student thinks that the cooling rate is directly proportional to the percentage of the surface area uncovered. He draws a graph of cooling rate against the percentage of uncovered area to investigate this. 

Describe how his graph line shows whether the rate of cooling and the percentage of uncovered surface area are directly proportional.

Students in other countries are doing the same experiment. 

State one factor they must keep the same to obtain similar readings.