B.1 Thermal energy transfers
Practice exam-style IB Physics questions for Thermal energy transfers, aligned with the syllabus and grouped by topic.
Question 1
A substance has a fixed volume but takes the shape of its container. What is the particle model description of this substance?
A.
Particles are close together and vibrate about fixed positions.
B.
Particles are far apart and move freely between collisions.
C.
Particles are close together and can move past neighbouring particles.
D.
Particles are stationary and arranged randomly.
Question 2
The temperature of a gas changes from 18 °C to 63 °C. What is the temperature change in kelvin?
A.
318 K
B.
108 K
C.
45 K
D.
336 K
Question 3
A warm copper block is placed in cooler water in an insulated container. What determines the direction of the resultant thermal energy transfer?
A.
The masses of the copper and water
B.
The densities of the copper and water
C.
The heat capacity of the container
D.
The temperature difference between the copper and water
Question 4
A metal cube has mass 0.54 kg and volume 2.0 × 10⁻⁴ m³. What is its density?
A.
2.7 × 10² kg m⁻³
B.
1.1 × 10³ kg m⁻³
C.
2.7 × 10³ kg m⁻³
D.
1.1 × 10⁴ kg m⁻³
Question 5
Two ideal gases are at the same Kelvin temperature. What must be the same for the particles of the two gases?
A.
Average speed
B.
Intermolecular potential energy
C.
Average translational kinetic energy
D.
Density
Question 6
What is included in the internal energy of a liquid?
A.
The total random kinetic energy and total intermolecular potential energy of the molecules
B.
Only the gravitational potential energy of the liquid
C.
The useful mechanical energy available from the liquid
D.
Only the random kinetic energy of the molecules
Question 7
Thermal energy from the Sun reaches Earth through space. What is the transfer mechanism?
A.
Evaporation, because particles leave the Sun’s surface
B.
Conduction, because particles collide across space
C.
Convection, because hot material rises from the Sun
D.
Thermal radiation, because electromagnetic waves can travel through a vacuum
Question 8
The absolute temperature of a black-body surface is increased from T to 2T. The surface area is unchanged. What is the factor increase in luminosity?
A.
2
B.
4
C.
8
D.
16
Question 9
A student finds that 75.0 cm³ of an oil has a mass of 61.5 g.
Convert the volume of oil to m³.
[1]
Calculate the density of the oil in kg m⁻³.
[1]
Question 10
A thermometer reads −12 °C inside a freezer.
State the corresponding Kelvin temperature.
[1]
The freezer warms to −5 °C. State the temperature change in kelvin.
[1]
Question 11
Ice at 0 °C is melting in a beaker. Energy is supplied at a constant rate, but the temperature remains constant until all the ice has melted. What is happening to the supplied energy during melting?
A.
It increases the intermolecular potential energy of the molecules.
B.
It decreases the total internal energy of the sample.
C.
It is completely transferred to the surroundings.
D.
It increases the average random kinetic energy of the molecules.
Question 12
A uniform rod conducts energy in steady state. The temperature difference across it is doubled and its length is halved. The material and cross-sectional area are unchanged. What happens to the rate of energy transfer by conduction?
A.
It is unchanged.
B.
It increases by a factor of 8.
C.
It increases by a factor of 4.
D.
It doubles.
Question 13
A star radiates uniformly. An observer moves from distance d to distance 3d from the star. What happens to the apparent brightness?
A.
It becomes three times as large.
B.
It becomes one third as large.
C.
It becomes nine times as large.
D.
It becomes one ninth as large.
Question 14
The peak wavelength in the black-body spectrum of a star is half that of the Sun. What can be inferred about the star’s surface temperature compared with the Sun’s surface temperature?
A.
It is one quarter as large.
B.
It is twice as large.
C.
It is four times as large.
D.
It is half as large.
Question 15
The temperature of a black body increases. What happens to its emission spectrum?
A.
The peak shifts to shorter wavelength and the area decreases.
B.
The peak shifts to shorter wavelength and the area increases.
C.
The peak wavelength stays fixed and the area increases.
D.
The peak shifts to longer wavelength and the area decreases.
Question 16
A sample of helium gas is at 310 K.
State what temperature measures for the particles of an ideal gas.
[1]
Calculate the average translational kinetic energy of a helium atom. Use kB = 1.38 × 10⁻²³ J K⁻¹.
[1]
Question 17
A beaker contains liquid water at 100 °C at standard pressure. Energy continues to be supplied.
State the phase change that occurs.
[1]
Explain why the temperature remains constant during this phase change.
[1]
Question 18
A 0.250 kg aluminium block is heated from 20.0 °C to 65.0 °C. The specific heat capacity of aluminium is 900 J kg⁻¹ K⁻¹.
State the temperature change of the block in K.
[1]
Calculate the energy transferred to the block.
[1]
Question 19
A radiator heats air near the floor of a room.
State why convection can occur in air but not in a solid wall.
[1]
Explain how a convection current forms above the radiator.
[1]
Question 20
A freezer removes energy from 0.12 kg of liquid water at 0 °C until it becomes ice at 0 °C. The specific latent heat of fusion of water is 3.34 × 10⁵ J kg⁻¹.
State why no specific heat capacity term is needed.
[1]
Calculate the energy removed.
[1]
Question 21
The intensity spectrum of a star has peak wavelength 4.8 × 10⁻⁷ m.
State Wien’s displacement law.
[1]
Calculate the surface temperature of the star.
[1]
Question 22
A fixed-power heater is used to heat a pure solid. The graph shows how the temperature of the sample varies with time.
Identify the time interval during which melting occurs.
[1]
Explain, using the particle model, why the temperature is constant during this interval.
[1]
The heater power is known and the mass of the sample is measured. State how the graph could be used to determine the specific latent heat of fusion.
[1]
Question 23
A student measures the mass of different volumes of a liquid. The graph shows mass against volume.
State what physical quantity is represented by the gradient of the graph.
[1]
Use the graph to determine the density of the liquid.
[1]
Suggest one reason why the plotted line may not pass exactly through the origin.
[1]
Question 24
A thermocouple is calibrated by placing one junction in melting ice and the other in water baths of known temperature. The graph shows thermocouple potential difference against temperature.
Describe the relationship shown by the calibration graph.
[1]
Use the graph to estimate the temperature corresponding to a given thermocouple potential difference marked on the graph.
[1]
Suggest two features of the graph or experiment that limit the precision of this temperature measurement.
[1]
Question 25
A small black body at 500 K is in a large room at 300 K. Other transfer mechanisms are negligible. What expression is proportional to the net radiative power lost by the body?
A.
(500 − 300)⁴
B.
300⁴
C.
500⁴ − 300⁴
D.
500⁴
Question 26
A gas sample is heated from 27 °C so that the average translational kinetic energy per molecule doubles. What is the final temperature?
A.
600 °C
B.
54 °C
C.
573 °C
D.
327 °C
Question 27
Two spherical black-body stars have the same surface temperature. Star X has twice the radius of star Y. What is the luminosity of X compared with Y?
A.
The same
B.
Twice as large
C.
Four times as large
D.
Sixteen times as large
Question 28
A glass window has area 1.8 m² and thickness 4.0 mm. The temperature difference between the inside and outside surfaces is 18 K. The thermal conductivity of the glass is 0.80 W m⁻¹ K⁻¹.
State one assumption needed to use the one-dimensional conduction equation.
[1]
Calculate the rate of energy transfer through the window.
[1]
Question 29
A copper rod of length 0.60 m and cross-sectional area 1.2 × 10⁻⁴ m² is maintained with its ends at 80 °C and 20 °C. The thermal conductivity of copper is 390 W m⁻¹ K⁻¹.
State the direction of energy transfer.
[1]
Calculate the steady-state rate of energy transfer along the rod.
[1]
Question 30
A spherical black-body asteroid has radius 12 m and surface temperature 240 K.
State the surface area to use in the Stefan–Boltzmann law.
[1]
Calculate the luminosity of the asteroid. Use σ = 5.67 × 10⁻⁸ W m⁻² K⁻⁴.
[1]
Question 31
A star has luminosity 3.9 × 10²⁶ W. Its apparent brightness at Earth is 1.4 × 10³ W m⁻².
Write down the relationship between luminosity, apparent brightness and distance.
[1]
Calculate the distance from Earth to the star.
[1]
Question 32
Two identical metal cans are filled with equal masses of hot water at the same initial temperature. One can is matt black and the other is shiny silver.
Predict which can cools faster when radiation is the dominant transfer mechanism.
[1]
Explain the prediction.
[1]
State one variable that should be controlled in the comparison.
[1]
Question 33
A metal rod is heated at one end. Temperature sensors along the rod record the steady-state temperature profile shown.
State what is meant by steady state in this experiment.
[1]
Use the graph to determine the temperature gradient in the central region of the rod.
[1]
Explain why insulation around the sides of the rod is needed for the conduction model used.
[1]
Question 34
Ice at 0 °C is added to warm water in an insulated cup. A table shows repeated measurements of the initial water temperature, final temperature and mass of ice melted.
| Trial | Mass water / g | Initial temp. / °C | Final temp. / °C | Mass ice melted / g |
|---|---|---|---|---|
| A | 200 | 47.5 | 27.0 | 38.4 |
| B | 210 | 51.0 | 28.4 | 43.8 |
| C | 190 | 44.0 | 26.2 | 31.9 |
| D | 205 | 53.2 | 29.1 | 45.4 |
| E | 195 | 49.0 | 27.8 | 38.4 |
Identify the trial with the largest temperature fall of the water.
[1]
For one trial, write the energy balance used to determine the specific latent heat of fusion of ice.
[1]
Suggest two reasons why the experimental value may differ from the accepted value.
[1]
Question 35
The graph shows black-body spectra for two stars, A and B.
Identify which star has the higher surface temperature.
[1]
Use the peak wavelength of star A from the graph to estimate its surface temperature.
[1]
Explain why the area under the spectrum is relevant to the luminosity of a star.
[1]
Question 36
A 0.150 kg copper block at 95.0 °C is placed in 0.200 kg of water at 20.0 °C in a well-insulated cup. The final temperature is 25.0 °C. The specific heat capacity of water is 4200 J kg⁻¹ K⁻¹.
Calculate the energy gained by the water.
[1]
Estimate the specific heat capacity of copper.
[1]
Question 37
A student measures the specific heat capacity of a metal block using an electric heater. The calculated value is higher than the accepted value.
Write an expression for the electrical energy supplied by the heater.
[1]
Suggest two experimental reasons why the calculated value may be too high.
[1]
State one improvement to reduce one of these effects.
[1]
Question 38
Star A has radius R and temperature T. Star B has radius 3R and temperature T/2. Both behave as black bodies.
State the equation for luminosity of a spherical black-body star.
[1]
Determine the ratio LB/LA.
[1]
Question 39
A table gives the luminosity and distance from Earth for four stars.
| Star | Luminosity / L☉ | Distance / pc |
|---|---|---|
| A | 4.0 | 4.0 |
| B | 40 | 20 |
| C | 200 | 80 |
| D | 800 | 120 |
Determine which star has the greatest apparent brightness at Earth.
[1]
student claims that the most luminous star must appear brightest. Use the data to evaluate this claim.
[1]
State one assumption needed when using b = L/(4πd²).
[1]
Question 40
A blackened metal sphere is heated and then allowed to cool in a vacuum chamber. The graph shows its temperature as a function of time. The chamber walls are at constant temperature.
Describe how the cooling rate changes as the sphere cools.
[1]
Explain this change using net radiative power.
[1]
Suggest why carrying out the experiment in a vacuum improves the test of the Stefan–Boltzmann model.
[1]
Question 41
A composite wall consists of two flat layers in contact. A table gives the thickness, thermal conductivity and area for each layer. The inside and outside surface temperatures are maintained constant.
| Layer | Thickness / m | Thermal conductivity / W m^-1 K^-1 | Area / m^2 | Exposed surface temp / °C |
|---|---|---|---|---|
| Inside layer | 0.020 | 0.17 | 12.0 | 22.0 |
| Outside layer | 0.120 | 0.72 | 12.0 | 6.0 |
State why the rate of energy transfer is the same through both layers at steady state.
[1]
Use the data to determine which layer has the larger temperature drop across it.
[1]
Suggest how changing the wall design could reduce the rate of energy transfer.
[1]
Question 42
A student determines the specific latent heat of fusion of ice by adding dry ice at 0 °C to warm water in an insulated cup.
Outline the energy transfers that occur after the ice is added.
[1]
Explain how the experiment can be used to determine the specific latent heat of fusion of ice, including two significant sources of uncertainty or error.
[1]
Question 43
A house loses thermal energy through its roof, walls and windows during winter.
Describe the three primary mechanisms of thermal energy transfer.
[1]
Discuss how features of the house can reduce energy loss by each mechanism.
[1]
Question 44
Water is heated in a power station boiler to produce steam that drives a turbine.
Describe the changes in molecular behaviour as water is heated from liquid water to steam.
[1]
Explain, using energy ideas, why phase change at constant temperature is useful in transferring energy in this process.
[1]
Question 45
The same mass of a substance can exist as a solid, liquid or gas.
Compare the particle arrangement and motion in solids and gases.
[1]
Explain how the molecular model accounts for differences in density, compressibility and thermal conduction between the three states.
[1]
Question 46
A solar absorber panel is tested using two surface finishes. The table gives the equilibrium panel temperature and incident solar power per unit area under the same conditions.
| Surface finish | Incident power / W m^-2 | Equilibrium temp / °C |
|---|---|---|
| Matt black | 820 | 68 |
| Shiny metallic | 820 | 91 |
Identify the surface finish with the greater ability to emit thermal radiation.
[1]
Use the Stefan–Boltzmann law qualitatively to explain why equilibrium temperature differs between the finishes.
[1]
Evaluate one limitation of using only L = σAT⁴ to model the panel temperature in this test.
[1]
Question 47
A star is modelled as a spherical black body. Its emission spectrum has peak wavelength λmax and its apparent brightness at Earth is b.
Explain how λmax can be used to determine the star’s surface temperature.
[1]
Evaluate how measurements of λmax and b, together with an estimate of the star’s radius, can be used to determine the distance to the star. Include assumptions in your answer.
[1]
Question 48
A flat solar collector is designed to absorb radiation from the Sun while minimizing thermal energy loss to its surroundings.
State two ways thermal energy can be lost from the collector surface.
[1]
Discuss how surface finish, insulation and operating temperature affect the efficiency of the collector.
[1]
Question 49
Two stars have black-body spectra. Star X has a higher peak intensity and a shorter peak wavelength than star Y.
Use Wien’s law to compare their surface temperatures.
[1]
Compare and contrast what can and cannot be inferred about their luminosities and apparent brightnesses from the spectra alone.
[1]
Question 50
An engineer compares two designs for an insulated container used to transport hot liquid. Design A uses a thick plastic wall with a shiny outer coating. Design B uses a thinner plastic wall, an evacuated gap and a matt black outer coating.
Explain how wall thickness and thermal conductivity affect conduction through the container wall.
[1]
Evaluate which design is likely to reduce the cooling rate more effectively, considering conduction, convection and radiation.
[1]
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