Transfer of Thermal Energy (CIE IGCSE Physics)

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1a1 mark

A student is investigating the rate of cooling of water under different conditions. A greater rate of cooling occurs if there is a greater change in the temperature during the same period of time.

Fig. 3.1 shows some of the apparatus.

p2-3a

The thermometer in Fig.3.2 shows the room temperature θ_Rat the beginning of the experiment. Record θ_R.

p2-2aii

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

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1b4 marks

The student pours 200 cm³ of hot water into the beaker.

She records the temperature θ of the hot water at time t = 0. She immediately starts a stopclock.

She continues recording the time and the temperature readings every 30 s. The readings are shown in Table 3.1.

Table 3.1

Beaker

t /	θ /
0	94
30	93
60	92
90	91
120	90
150	89

Table 3.2

Can

t /	θ /
0	93
30	91
60	90
90	89
120	88
150	87

The student repeats the procedure using a metal can, painted matt black, in place of the beaker.

The readings are shown in Table 3.2.

(i)

Complete the column headings in Table 3.1 and in Table 3.2.

[1]

(ii)

Look carefully at the readings in Table 3.1 and in Table 3.2.

Tick the box to show your conclusion from the readings.

□

The water in the beaker has a greater rate of cooling than the water in the can.

□

The water in the beaker has a smaller rate of cooling than the water in the can.

□

There is no significant difference between the rates of cooling of the water in the beaker and the can.

[1]

(iii)

Justify your conclusion by reference to the readings.

[2]

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1c4 marks

A student in another school carries out the experiment and reports that the rate of cooling of the water in the can is different from the rate of cooling of the water in the beaker. He plans a change to the experiment to find out whether this difference in the rates of cooling is caused by

the matt black surface of the can being a better radiator of thermal energy than the shiny surface of the beaker
the metal of the can being a better conductor of thermal energy than the material of the beaker.

(i)

Suggest two suitable changes to the apparatus that the student could make.

[2]

(ii)

Suggest two variables that should be controlled in order to make the experiment a fair test.

[2]

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1d1 mark

State one precaution that you would take in order to record accurate temperature readings.

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3a1 mark

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

They are using the apparatus shown in Fig. 2.1. q2-a

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

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

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3b2 marks

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]

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3c3 marks

(i)

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

x_{1} = \frac{θ_{0} - θ_{90}}{T}

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

x_{2} = \frac{θ_{90} - θ_{180}}{T}

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

x_{3} = \frac{θ_{180} - θ_{270}}{T}

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

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

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3d2 marks

(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]

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3e3 marks

(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]

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4a1 mark

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.

p3-2a

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

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

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4b2 marks

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

p3-1b

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4c2 marks

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.

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4d2 marks

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.

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4e4 marks

(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

$x_{A} = \frac{θ_{0} - θ_{180}}{T}$

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]

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6a3 marks

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_Bof 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

	beaker A with 200 cm³ of water	beaker B with 100 cm³ of water
t/	θ_A/	θ_B/
0
	85.0	86.0
	83.0	83.0
	81.5	80.5
	80.0	78.0
	78.5	76.0
	77.5	74.5

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6b1 mark

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

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6c2 marks

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.

How did you do?

6d2 marks

(i)

Using the results for 100 cm³of 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

x_{1} = \frac{θ_{0} - θ_{90}}{t}

where t = 90 s and θ₀and 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

$x_{2} = \frac{θ_{90} - θ_{180}}{t}$

where t = 90 s and θ₉₀ and θ₁₈₀are the temperatures at time 90 s and at time 180 s. Include the unit for the rate of cooling.

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

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6e1 mark

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.

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6f2 marks

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.

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