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B.1 Thermal energy transfers

Practice exam-style IB Physics questions for Thermal energy transfers, aligned with the syllabus and grouped by topic.

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Question 1
SL • Paper 1A
Easy
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SL • Paper 1A
Easy
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A liquid is heated from 18 ∘C18\ ^\circ\text{C} to 45 ∘C45\ ^\circ\text{C}.

What are the temperature change and the final temperature on the Kelvin scale?

A.

temperature change 27 K27\ \text{K}; final temperature 45 K45\ \text{K}

B.

temperature change 300 K300\ \text{K}; final temperature 318 K318\ \text{K}

C.

temperature change 300 K300\ \text{K}; final temperature 45 K45\ \text{K}

D.

temperature change 27 K27\ \text{K}; final temperature 318 K318\ \text{K}

Question 2
SL • Paper 1A
Easy
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SL • Paper 1A
Easy
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A mass of 0.20 kg0.20\ \text{kg} of ice at 0 ∘C0\ ^\circ\text{C} melts completely at constant temperature. The specific latent heat of fusion of ice is 3.3×105 J kg−13.3\times10^5\ \text{J kg}^{-1}.

What is the energy transferred to the ice?

A.

3.3×105 J3.3\times10^5\ \text{J}

B.

1.65×105 J1.65\times10^5\ \text{J}

C.

6.6×103 J6.6\times10^3\ \text{J}

D.

6.6×104 J6.6\times10^4\ \text{J}

Question 3
SL • Paper 1A
Easy
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SL • Paper 1A
Easy
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A metal cube has sides of length 2.0 cm2.0\ \text{cm} and mass 64 g64\ \text{g}.

What is the density of the metal in SI units?

A.

8.0×103 kg m−38.0\times10^3\ \text{kg m}^{-3}

B.

80 kg m−380\ \text{kg m}^{-3}

C.

8.0 kg m−38.0\ \text{kg m}^{-3}

D.

8.0×104 kg m−38.0\times10^4\ \text{kg m}^{-3}

Question 4
SL • Paper 1A
Easy
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SL • Paper 1A
Easy
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Samples of helium and neon gas are at the same Kelvin temperature.

What is true about the average translational kinetic energy per atom in the two samples?

A.

It is the same for both gases because it depends only on Kelvin temperature.

B.

It is greater for neon because neon atoms have larger mass.

C.

It is greater for helium because helium atoms have smaller mass.

D.

It is zero for both gases unless the gases are changing phase.

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Question 5
SL • Paper 1A
Easy
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SL • Paper 1A
Easy
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Ice at 0 ∘C0\ ^\circ\text{C} is melting while energy is supplied at a constant rate.

What happens to the average random kinetic energy of the molecules and to the intermolecular potential energy during melting?

A.

Average random kinetic energy decreases; intermolecular potential energy increases.

B.

Average random kinetic energy increases; intermolecular potential energy remains constant.

C.

Average random kinetic energy increases; intermolecular potential energy decreases.

D.

Average random kinetic energy remains constant; intermolecular potential energy increases.

Question 6
HL • Paper 1A
Easy
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HL • Paper 1A
Easy
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A black-body surface has constant area. Its absolute temperature increases from 300 K300\ \text{K} to 600 K600\ \text{K}.

By what factor does the power radiated increase?

A.

44

B.

88

C.

22

D.

1616

Question 7
HL • Paper 1A
Easy
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HL • Paper 1A
Easy
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Two identical detectors observe the same star. Detector X is at distance dd from the star and detector Y is at distance 3d3d.

What is the apparent brightness measured by detector Y in terms of the apparent brightness bb measured by detector X?

A.

9b9b

B.

b9\frac{b}{9}

C.

3b3b

D.

b3\frac{b}{3}

Question 8
SL • Paper 2
Easy
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SL • Paper 2
Easy
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A rectangular aluminium block has a mass of 216 g216\ \text{g} and a volume of 80.0 cm380.0\ \text{cm}^3.

A

Calculate the density of the block in SI units.

[2]
B

Explain, using the particle model, why the density of a gas is much smaller than that of the solid block.

[1]

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Question 9
SL • Paper 2
Easy
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SL • Paper 2
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A sample of solid wax is heated at a constant rate. Its temperature is recorded as it melts.

Heating curve of wax during melting.
A

State what happens to the temperature of the wax during the horizontal section of the graph.

[1]
B

Explain, in terms of molecular energy, why energy is transferred to the wax during this section although its temperature does not increase.

[2]
Question 10
SL • Paper 2
Easy
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SL • Paper 2
Easy
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A vacuum flask contains hot tea. The flask has a double wall with a vacuum between the walls, a shiny inner surface and a plastic stopper.

A labelled cross-section of a vacuum flask showing hot liquid, an inner wall, an outer wall, a vacuum gap, a shiny silvered surface and a plastic stopper. The diagram should not include labels naming the mechanisms of thermal energy transfer.
A

Explain how the vacuum gap reduces thermal energy transfer.

[1]
B

Explain how the shiny surface reduces thermal energy transfer.

[1]
C

Suggest why the stopper is made from plastic rather than metal.

[1]
Question 11
SL • Paper 1A
Medium
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SL • Paper 1A
Medium
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A beaker of water is heated from below at its centre.

The diagram that best represents the natural convection current in the water after heating begins is

A.
A simple cross-section of a beaker containing water with a small heater centred under the base. Draw arrows showing water rising vertically above the heater, spreading outward near the surface, sinking down near both side walls, and flowing inward along the bottom back toward the heater. Use the same line weight and arrow style as the other options.
B.
A simple cross-section of a beaker containing water with a small heater centred under the base. Draw arrows in the water forming a single horizontal loop mainly around the middle height of the water, with little or no upward motion above the heater and little or no downward motion at the sides. Use the same line weight and arrow style as the other options.
C.
A simple cross-section of a beaker containing water with a small heater centred under the base. Draw arrows in the water showing fluid moving downward above the heater, spreading outward along the bottom, rising near the side walls, and returning inward along the surface. Use the same line weight and arrow style as the other options.
D.
A simple cross-section of a beaker containing water with a small heater centred under the base. Draw two small circular loops, one on each side of the beaker, with arrows not clearly rising above the heater and not showing a continuous return flow along the base to the heater. Use the same line weight and arrow style as the other options.
Question 12
HL • Paper 1A
Medium
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HL • Paper 1A
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A slab conducts thermal energy in steady state. The temperature difference across it is unchanged. A second slab is made of the same material, has twice the cross-sectional area and half the thickness.

What is the ratio

rate for second slabrate for first slab\frac{\text{rate for second slab}}{\text{rate for first slab}}

for conduction through the slabs?

A.

11

B.

88

C.

44

D.

22

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Question 13
HL • Paper 1A
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HL • Paper 1A
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The peak wavelength in the emission spectrum of a star is 5.0×10−7 m5.0\times10^{-7}\ \text{m}.

Using Wien's displacement law, what is the approximate surface temperature of the star?

A.

5.8×103 K5.8\times10^3\ \text{K}

B.

1.7×10−4 K1.7\times10^{-4}\ \text{K}

C.

1.5×103 K1.5\times10^3\ \text{K}

D.

1.7×106 K1.7\times10^6\ \text{K}

Question 14
HL • Paper 1A
Medium
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HL • Paper 1A
Medium
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The dotted curve represents the black-body emission spectrum of an object at temperature TT. A second identical black body is at a higher temperature.

The diagram that correctly shows the spectrum of the second black body as a solid curve is

A.
A graph with vertical axis labelled intensity and horizontal axis labelled wavelength. Include a dotted black-body spectrum curve as a reference. Draw the solid curve with its peak shifted to a shorter wavelength than the dotted curve but with a lower maximum and smaller area under the curve. Keep styling, axes and curve thickness comparable with the other options.
B.
A graph with vertical axis labelled intensity and horizontal axis labelled wavelength. Include a dotted black-body spectrum curve as a reference. Draw the solid curve with a higher maximum than the dotted curve but with its peak shifted to a longer wavelength. Keep styling, axes and curve thickness comparable with the other options.
C.
A graph with vertical axis labelled intensity and horizontal axis labelled wavelength. Include a dotted black-body spectrum curve as a reference. Draw the solid curve with a higher maximum than the dotted curve, a larger area under the curve, and its peak shifted to a shorter wavelength. Keep styling, axes and curve thickness comparable with the other options.
D.
A graph with vertical axis labelled intensity and horizontal axis labelled wavelength. Include a dotted black-body spectrum curve as a reference. Draw the solid curve with a lower maximum than the dotted curve and with its peak shifted to a longer wavelength. Keep styling, axes and curve thickness comparable with the other options.
Question 15
SL • Paper 2
Medium
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SL • Paper 2
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A fixed mass of ideal gas is heated from 27 ∘C27\ ^\circ\text{C} to 177 ∘C177\ ^\circ\text{C}.

A

State the initial and final temperatures of the gas in kelvin.

[1]
B

Calculate the ratio of the final average translational kinetic energy of a molecule to its initial average translational kinetic energy.

[2]
C

Explain why doubling the Celsius temperature would not double the average kinetic energy of the molecules.

[1]
Question 16
SL • Paper 2
Medium
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SL • Paper 2
Medium
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A metal block of mass 0.850 kg0.850\ \text{kg} is heated electrically. A 40.0 W40.0\ \text{W} heater is operated for 300 s300\ \text{s}. The temperature of the block increases from 18.0 ∘C18.0\ ^\circ\text{C} to 32.0 ∘C32.0\ ^\circ\text{C}.

A

Calculate the specific heat capacity of the metal, assuming that all the electrical energy is transferred to the block.

[3]
B

Suggest how thermal energy transfer to the surroundings affects the value calculated in (a).

[1]

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Question 17
SL • Paper 2
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SL • Paper 2
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A single glass window has area 1.20 m21.20\ \text{m}^2 and thickness 4.00 mm4.00\ \text{mm}. The thermal conductivity of the glass is 0.80 W m−1K−10.80\ \text{W m}^{-1}\text{K}^{-1}. The temperature of the inside surface is 20.0 ∘C20.0\ ^\circ\text{C} and the temperature of the outside surface is 5.0 ∘C5.0\ ^\circ\text{C}.

A

Calculate the magnitude of the rate of thermal energy transfer through the window by conduction.

[3]
B

State the direction of the resultant thermal energy transfer and relate this to the sign in the conduction equation.

[1]
Question 18
HL • Paper 2
Medium
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HL • Paper 2
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The emission spectrum of a star is approximated by a black-body spectrum. The peak wavelength of the spectrum is 480 nm480\ \text{nm}.

Black-body spectrum of a star.
A

Calculate the surface temperature of the star.

[2]
B

Explain how the peak wavelength would change for a cooler star.

[1]
Question 19
SL • Paper 1B
Medium
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SL • Paper 1B
Medium
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A student investigates three samples of matter at room temperature. The mass and volume of each sample are shown in the table.

Sample

Mass / kg

Volume / m3m^3

State

Particle spacing

A

2.70

1.00×10−31.00 \times 10^{-3}

solid

very closely packed

B

0.158

2.00×10−42.00 \times 10^{-4}

liquid

close together

C

0.158

2.00×10−12.00 \times 10^{-1}

gas

far apart

A

Calculate the density of sample B.

[2]
B

Using the particle model, explain why sample C has a much lower density than sample B.

[2]
Question 20
SL • Paper 1B
Medium
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SL • Paper 1B
Medium
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A thermocouple is calibrated by placing one junction in ice water and the other junction in water baths of known temperature. The calibration graph shows the thermocouple potential difference against Celsius temperature.

Calibration graph of thermocouple potential difference against temperature.
A

Use the graph to determine the temperature corresponding to a potential difference of 1.50 mV1.50\ \text{mV}. Give your answer in kelvin.

[2]
B

The thermocouple reading increases from 0.80 mV0.80\ \text{mV} to 1.10 mV1.10\ \text{mV} during a heating experiment. Explain why the temperature change has the same numerical value in kelvin and in degrees Celsius.

[1]
C

Suggest one change to the calibration procedure that would reduce random uncertainty in the graph.

[1]

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Question 21
SL • Paper 1B
Medium
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SL • Paper 1B
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A small crystal of dye is placed at the bottom of a beaker of water near a heater. The diagram shows the observed motion of the coloured water after heating begins.

An annotated side-view diagram of a beaker of water on a heater. Arrows show coloured warm water rising above the heater, moving sideways near the top surface, sinking near the cooler sides and returning along the bottom. A thermometer near the heater reads higher than one near the side. The heater, cooler side region, rising current and sinking current are labelled.
A

Describe why the water near the heater begins to rise.

[2]
B

Identify the mechanism of thermal energy transfer shown by the circulating arrows.

[1]
C

Explain why this type of circulation cannot occur in a solid.

[1]
Question 22
HL • Paper 1A
Medium
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HL • Paper 1A
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Two spherical black-body stars A and B have the same radius. The surface temperature of A is twice that of B. Star A is four times as far from Earth as star B.

What is the ratio of their apparent brightnesses at Earth, bA/bBb_A/b_B?

A.

11

B.

14\frac{1}{4}

C.

44

D.

1616

Question 23
HL • Paper 2
Medium
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HL • Paper 2
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A spherical object is modelled as a black body. Its radius is 0.400 m0.400\ \text{m} and its surface temperature is 600 K600\ \text{K}. Use σ=5.67×10−8 W m−2K−4\sigma=5.67\times10^{-8}\ \text{W m}^{-2}\text{K}^{-4}.

A

Calculate the luminosity of the object.

[3]
B

Determine the factor by which the luminosity changes if the absolute temperature is increased by 10%10\% while the radius remains constant.

[1]
Question 24
HL • Paper 2
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HL • Paper 2
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A star has luminosity 3.8×1028 W3.8\times10^{28}\ \text{W}. The apparent brightness of the star measured at Earth is 1.2×10−8 W m−21.2\times10^{-8}\ \text{W m}^{-2}. Assume that the star radiates uniformly in all directions.

A

Calculate the distance from Earth to the star.

[3]
B

State the apparent brightness of an identical star at twice this distance, in terms of the measured apparent brightness.

[1]

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Question 25
HL • Paper 2
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HL • Paper 2
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A flat layer of insulating material has thickness 6.0 cm6.0\ \text{cm}, cross-sectional area 2.5 m22.5\ \text{m}^2 and thermal conductivity 0.040 W m−1K−10.040\ \text{W m}^{-1}\text{K}^{-1}. In steady state, the temperature difference across the layer is 18 K18\ \text{K}.

A simple slab diagram showing a flat insulating layer of uniform thickness, with the two faces at different temperatures. Arrows indicate the direction of thermal energy transfer through the layer, and labels identify area, thickness and temperature difference without giving numerical values.
A

Calculate the rate of thermal energy transfer through the layer.

[2]
B

Determine the time taken for 2.7×105 J2.7\times10^5\ \text{J} to be transferred through the layer at this rate.

[1]
Question 26
SL • Paper 1B
Medium
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SL • Paper 1B
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Energy is supplied at a constant rate to a sample of water initially in the solid phase. The graph shows the temperature of the sample against energy supplied.

Temperature of a water sample against energy supplied.
A

Identify the phase change occurring during the first horizontal section of the graph.

[1]
B

The mass of the sample is 0.250 kg0.250\ \text{kg}. Use the liquid-water section of the graph to determine the specific heat capacity of water.

[2]
C

Explain, in terms of internal energy, why the temperature remains constant during a horizontal section although energy is being supplied.

[2]
Question 27
SL • Paper 1B
Medium
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SL • Paper 1B
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Ice at 0∘C0^\circ\text{C} is added to warm water in a light insulated cup. The table gives the measurements for one trial. Take the specific heat capacity of water to be 4.20×103 J kg−1K−14.20\times10^3\ \text{J kg}^{-1}\text{K}^{-1}.

Quantity

Unit

Value

Mass of warm water

kg

0.200

Initial temperature of warm water

∘C^\circ\text{C}

35

Mass of ice added

kg

0.060

Initial temperature of ice

∘C^\circ\text{C}

0

Final temperature of mixture

∘C^\circ\text{C}

10

A

State the direction of the resultant thermal energy transfer before thermal equilibrium is reached.

[1]
B

Use the data to calculate the specific latent heat of fusion of ice.

[3]
C

Suggest why the ice is dried before being added to the cup.

[1]
Question 28
SL • Paper 1B
Medium
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SL • Paper 1B
Medium
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A long uniform rod is heated at one end and cooled at the other. The temperature along the rod is measured after steady state has been reached. The cross-sectional area of the rod is 2.0×10−4 m22.0\times10^{-4}\ \text{m}^2 and the thermal conductivity is 15 W m−1K−115\ \text{W m}^{-1}\text{K}^{-1}.

Steady-state temperature profile along a uniform rod.
A

State the direction of thermal energy transfer in the rod.

[1]
B

Determine the magnitude of the temperature gradient in the rod.

[1]
C

Calculate the rate of thermal energy transfer along the rod.

[2]
D

Explain why the readings should be taken only after steady state is reached.

[1]

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Question 29
HL • Paper 1B
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HL • Paper 1B
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The graph shows the mean translational kinetic energy per molecule for two different ideal gases as a function of absolute temperature.

Mean translational kinetic energy per molecule for helium and neon as a function of absolute temperature.
A

Use E‾k=32kBT\overline{E}_k=\dfrac{3}{2}k_BT to calculate the mean translational kinetic energy of a molecule at 600 K600\ \text{K}. Use kB=1.38×10−23 J K−1k_B=1.38\times10^{-23}\ \text{J K}^{-1}.

[2]
B

The mass of a neon atom is about five times the mass of a helium atom. Determine the ratio vHevNe\dfrac{v_\text{He}}{v_\text{Ne}} for atoms with the same mean translational kinetic energy.

[2]
Question 30
HL • Paper 2
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HL • Paper 2
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A small matt black sphere of radius 5.0 cm5.0\ \text{cm} is at a temperature of 500 K500\ \text{K}. It is treated as a black body and other thermal energy transfer mechanisms are neglected. Use σ=5.67×10−8 W m−2K−4\sigma=5.67\times10^{-8}\ \text{W m}^{-2}\text{K}^{-4}.

A

Calculate the energy radiated by the sphere in 120 s120\ \text{s}.

[3]
B

Suggest why the actual decrease in internal energy of the sphere during this time may be less than the value calculated in (a).

[1]
Question 31
HL • Paper 2
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HL • Paper 2
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In an insulated container, 0.150 kg0.150\ \text{kg} of ice at 0 ∘C0\ ^\circ\text{C} is added to 0.400 kg0.400\ \text{kg} of water at 60 ∘C60\ ^\circ\text{C}. The specific latent heat of fusion of ice is 3.34×105 J kg−13.34\times10^5\ \text{J kg}^{-1} and the specific heat capacity of water is 4200 J kg−1K−14200\ \text{J kg}^{-1}\text{K}^{-1}.

A

Show that all the ice melts.

[2]
B

Calculate the final equilibrium temperature of the water.

[2]
Question 32
HL • Paper 1B
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HL • Paper 1B
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Two identical metal cans are filled with equal masses of hot water. One can has a matt black surface and the other has a shiny white surface. The cooling curves are shown.

Cooling curves for matt black and shiny white cans.
A

State which surface is the better emitter of thermal radiation.

[1]
B

Use the initial gradients of the curves to estimate the ratio PblackPshiny\dfrac{P_\text{black}}{P_\text{shiny}} of the initial rates of thermal energy loss.

[2]
C

Evaluate whether this experiment by itself tests only the Stefan-Boltzmann law.

[2]

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Question 33
HL • Paper 1B
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HL • Paper 1B
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A detector measures the apparent brightness of a star. The distance to the star is determined independently. The table gives the data. Take the luminosity of the Sun to be 3.83×1026 W3.83\times10^{26}\ \text{W}.

Distance / m

Apparent brightness / W m−2^{-2}

1.10×10171.10 \times 10^{17}

3.20×10−83.20 \times 10^{-8}

A

State the relationship between apparent brightness and distance for a source of constant luminosity.

[1]
B

Calculate the luminosity of the star in watts and in solar luminosities.

[2]
C

The percentage uncertainty in the distance is 10%10\%. State the approximate percentage uncertainty this gives in the luminosity, ignoring uncertainty in bb.

[1]
D

Explain how a star of greater luminosity can have a smaller apparent brightness than this star.

[1]
Question 34
HL • Paper 1B
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HL • Paper 1B
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The graph shows idealized black-body emission spectra for two stars, A and B. The vertical scale is intensity per unit wavelength in arbitrary units.

Idealized black-body emission spectra for stars A and B.
A

Use Wien's displacement law to determine the surface temperature of star A.

[2]
B

The peak wavelength of star B is twice that of star A. Compare the power radiated per unit surface area by star A with that by star B.

[2]
Question 35
SL • Paper 2
Hard
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SL • Paper 2
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A sealed cylinder contains helium gas at 18 ∘C18\ ^\circ\text{C}. The gas is warmed until its temperature is 72 ∘C72\ ^\circ\text{C}. The cylinder volume is constant.

A simple diagram of a sealed rigid cylinder containing gas particles. Two states are shown side by side: the same cylinder before and after heating. The after-heating cylinder should show particle motion arrows that are generally longer than in the initial cylinder, without implying any change in volume or number of particles.
A

The gas temperature is considered on the Kelvin scale.

I.

Determine the initial temperature of the gas in kelvin.

[1]
II.

Calculate the ratio E‾k,2E‾k,1\dfrac{\overline{E}_{k,2}}{\overline{E}_{k,1}} of the average translational kinetic energy of a helium atom after heating to that before heating.

[2]
B

Explain why doubling a temperature expressed in degrees Celsius would not double the average translational kinetic energy of the atoms.

[2]
C

Explain the change in internal energy of the gas during the heating process.

[2]
Question 36
SL • Paper 2
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SL • Paper 2
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Two identical metal cans contain equal masses of hot water initially at the same temperature. Can A has a matt black outer surface. Can B has a shiny silver outer surface. Both cans are placed in still air in the same room.

Cooling curves for two identical cans in still air, with room temperature shown.
A

The cooling curves for the two cans are compared.

I.

State which can has the greater initial rate of cooling.

[1]
II.

Explain this difference in terms of thermal radiation.

[2]
B

Explain why the rate of cooling of either can decreases as it approaches room temperature.

[2]
C

Evaluate whether this experiment isolates radiation as the only mechanism of thermal energy transfer.

[2]

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Question 37
HL • Paper 1B
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HL • Paper 1B
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A double-glazed window is modelled as two conducting layers in series: glass and trapped air. The indoor temperature is 293 K293\ \text{K} and the outdoor temperature is 273 K273\ \text{K}. The window area is 1.20 m21.20\ \text{m}^2.

Quantity

Value

Units

Window area

1.20

m2m^2

Indoor temperature

293

KK

Outdoor temperature

273

KK

Glass thickness

0.0040

mm

Glass thermal conductivity

0.80

W m−1 K−1W\ m^{-1}\ K^{-1}

Trapped air thickness

0.012

mm

Trapped air thermal conductivity

0.024

W m−1 K−1W\ m^{-1}\ K^{-1}

A

Determine the steady rate of thermal energy transfer through the window using the layer data.

[3]
B

Determine the temperature drop across the glass layer.

[1]
C

Use your answer to suggest why trapped air is effective in reducing conduction through a window.

[1]
Question 38
HL • Paper 1B
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HL • Paper 1B
Hard
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A small black metal plate in a vacuum absorbs radiation from a lamp. The plate is thermally isolated except for radiation exchange with surroundings at 295 K295\ \text{K}. The area of one side is 3.00×10−2 m23.00\times10^{-2}\ \text{m}^2, and the plate emits radiation from both sides. The absorbed power is 40.0 W40.0\ \text{W} and the emitting area is 3.00×10−2 m23.00\times10^{-2}\ \text{m}^2. Use σ=5.67×10−8 W m−2K−4\sigma=5.67\times10^{-8}\ \text{W m}^{-2}\text{K}^{-4}.

An annotated diagram of a black plate inside an evacuated chamber. A lamp shines on the plate, and arrows indicate absorbed radiation from the lamp and emitted thermal radiation from both sides of the plate. The labelled emitting area refers to one side of the plate, and the surrounding chamber temperature, plate area and absorbed power are labelled. A small inset energy-flow diagram shows equilibrium when absorbed power equals net radiative loss.
A

State the condition for the plate to be in thermal equilibrium.

[1]
B

Calculate the equilibrium temperature of the plate, treating it as a black body.

[3]
C

Suggest how the equilibrium temperature would change if the plate were replaced by a shiny plate of the same area, assuming the same absorbed lamp power.

[1]
Question 39
SL • Paper 2
Hard
Calculator Permitted
SL • Paper 2
Hard
Calculator Permitted

A student determines the specific latent heat of fusion of ice by adding ice at 0 ∘C0\ ^\circ\text{C} to water in a light insulated cup. Initially the cup contains 0.240 kg0.240\ \text{kg} of water at 34.0 ∘C34.0\ ^\circ\text{C}. The final equilibrium temperature is 12.0 ∘C12.0\ ^\circ\text{C}. The mass of ice added is 0.058 kg0.058\ \text{kg}.

The specific heat capacity of water is 4.18×103 J kg−1 K−14.18\times10^3\ \text{J kg}^{-1}\ \text{K}^{-1}.

An insulated cup calorimeter containing water with a thermometer inserted. Several small ice pieces are shown being added. Labels should identify the insulated cup, water, thermometer and ice at 0 °C; the diagram must not show the calculation result.
A

The energy transfers in the cup are modelled as occurring only between the water and the ice.

I.

Calculate the energy transferred from the original water as it cools.

[2]
II.

Determine the specific latent heat of fusion of the ice.

[3]
B

Explain, using the molecular model, why the temperature of the ice-water mixture remains at 0 ∘C0\ ^\circ\text{C} while ice is melting.

[2]
C

Suggest one reason why the experimental value of LL may be lower than the accepted value, even if the temperature readings are accurate.

[1]
Question 40
SL • Paper 2
Hard
Calculator Permitted
SL • Paper 2
Hard
Calculator Permitted

A house wall contains a uniform insulating slab of area 12.0 m212.0\ \text{m}^2 and thickness 0.080 m0.080\ \text{m}. The inside surface of the slab is at 19 ∘C19\ ^\circ\text{C} and the outside surface is at 4 ∘C4\ ^\circ\text{C}. The thermal conductivity of the slab is 0.040 W m−1 K−10.040\ \text{W m}^{-1}\ \text{K}^{-1}.

A cross-section of a flat house wall showing a uniform insulating slab. The inside face is labelled warm and the outside face cold. The thickness is indicated by a double-headed arrow across the slab, and the surface area is indicated separately. A heat-flow arrow points from inside to outside.
A

Consider steady-state conduction through the slab.

I.

Determine the magnitude of the temperature gradient in the slab.

[1]
II.

Calculate the rate of thermal energy transfer through the slab.

[3]
B

Explain, in terms of particle motion, why energy is transferred from the inside surface to the outside surface.

[2]
C

Discuss one limitation of applying the slab equation to a real house wall.

[1]

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Question 41
SL • Paper 2
Hard
Calculator Permitted
SL • Paper 2
Hard
Calculator Permitted

A 0.150 kg0.150\ \text{kg} sample of a solid is heated at a constant rate of 60.0 W60.0\ \text{W}. The graph shows the variation of temperature of the sample with time. The sample begins below its melting temperature and later becomes a liquid.

Temperature–time heating curve for a sample.
A

From the graph, the solid warms from 10 ∘C10\ ^\circ\text{C} to 40 ∘C40\ ^\circ\text{C} in 90 s90\ \text{s}. It then melts at 40 ∘C40\ ^\circ\text{C} for 180 s180\ \text{s}.

I.

Determine the specific heat capacity of the solid.

[2]
II.

Determine the specific latent heat of fusion of the sample.

[2]
III.

State what can be inferred about the average kinetic energy of the particles during the plateau.

[1]
B

After melting, the liquid warms more slowly than the solid for the same heater power. Explain what this implies about the liquid.

[2]
C

Suggest one experimental reason why the calculated latent heat would be larger than the true value.

[1]
Question 42
SL • Paper 2
Hard
Calculator Permitted
SL • Paper 2
Hard
Calculator Permitted

A small spherical asteroid is modelled as a black body of radius 3.0 m3.0\ \text{m} and uniform surface temperature 260 K260\ \text{K}. Take the Stefan-Boltzmann constant to be 5.67×10−8 W m−2 K−45.67\times10^{-8}\ \text{W m}^{-2}\ \text{K}^{-4}.

A spherical asteroid radiating uniformly into space. The surface area is represented by outward arrows from all sides of the sphere. A distant detector is shown on one side with radiation spreading over an expanding sphere.
A

The asteroid emits thermal radiation as a black body.

I.

Calculate the surface area of the asteroid.

[1]
II.

Determine the luminosity of the asteroid.

[3]
III.

State the factor by which the luminosity changes if the temperature is doubled while the radius is unchanged.

[1]
B

A detector is placed far from the asteroid. Explain why the apparent brightness decreases with distance from the asteroid.

[2]
C

Discuss one reason why the black-body model may not give the exact luminosity of the asteroid.

[1]
Question 43
HL • Paper 2
Hard
Calculator Permitted
HL • Paper 2
Hard
Calculator Permitted

A star is modelled as a spherical black body. Its surface temperature is 5800 K5800\ \text{K} and its radius is 6.9×108 m6.9\times10^8\ \text{m}. An observer measures its apparent brightness to be 1.4×103 W m−21.4\times10^3\ \text{W m}^{-2}. Take σ=5.67×10−8 W m−2 K−4\sigma=5.67\times10^{-8}\ \text{W m}^{-2}\ \text{K}^{-4}.

A star radiating uniformly into space with a distant observer or detector. The star radius is indicated, and a large spherical wavefront centred on the star is shown to represent radiation spreading over area $4\pi d^2$.
A

The luminosity of the star is inferred from its radius and temperature.

I.

Calculate the luminosity of the star.

[3]
II.

Determine the distance from the star to the observer.

[2]
B

A second star has the same apparent brightness but a lower surface temperature. Discuss why this observation alone is not sufficient to conclude that the second star has the same luminosity.

[2]
C

Evaluate one assumption made when the star is treated as a black body.

[1]
Question 44
HL • Paper 2
Hard
Calculator Permitted
HL • Paper 2
Hard
Calculator Permitted

The black-body emission spectra of two stars, X and Y, are observed. Star X has a peak wavelength of 4.8×10−7 m4.8\times10^{-7}\ \text{m}. Star Y has a peak wavelength of 7.2×10−7 m7.2\times10^{-7}\ \text{m}.

Two continuous black-body spectra on shared axes.
A

The temperatures of the stars are determined from their peak wavelengths.

I.

Calculate the surface temperature of star X.

[2]
II.

Calculate the surface temperature of star Y.

[2]
B

Compare and contrast the spectra of stars X and Y using the black-body model.

[3]

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Question 45
HL • Paper 2
Hard
Calculator Permitted
HL • Paper 2
Hard
Calculator Permitted

In a demonstration, steam at 100 ∘C100\ ^\circ\text{C} is passed into 0.500 kg0.500\ \text{kg} of water initially at 20.0 ∘C20.0\ ^\circ\text{C} in an insulated container. The final equilibrium temperature is 55.0 ∘C55.0\ ^\circ\text{C}. The specific heat capacity of water is 4.18×103 J kg−1 K−14.18\times10^3\ \text{J kg}^{-1}\ \text{K}^{-1}. The specific latent heat of vaporization of water is 2.26×106 J kg−12.26\times10^6\ \text{J kg}^{-1}.

An insulated container of water with a steam inlet tube entering below the water surface and a thermometer. Steam is shown entering and condensing in the water. Labels identify steam at 100 °C, water and thermometer; the diagram should not reveal the mass of condensed steam.
A

Assume all the steam condenses and then the condensed water cools to the final temperature.

I.

Calculate the energy gained by the original water.

[2]
II.

Determine the mass of steam that condenses.

[3]
B

Explain, in molecular terms, why condensation releases energy while the temperature of the steam-water mixture can remain at 100 ∘C100\ ^\circ\text{C} during the phase change at standard pressure.

[2]
C

Evaluate one safety or experimental limitation of using steam in this calorimetry method.

[1]
Question 46
HL • Paper 2
Hard
Calculator Permitted
HL • Paper 2
Hard
Calculator Permitted

A thermocouple produces a potential difference VV that is used to measure temperature. The thermocouple is calibrated using fixed-temperature baths. Over the range tested, the calibration is assumed to be linear.

Thermocouple calibration data showing potential difference against temperature.
A

During calibration, V=0.00 mVV=0.00\ \text{mV} at 0 ∘C0\ ^\circ\text{C} and V=4.10 mVV=4.10\ \text{mV} at 100 ∘C100\ ^\circ\text{C}.

I.

Determine the sensitivity of the thermocouple in mV ∘C−1\text{mV}\ ^\circ\text{C}^{-1}.

[1]
II.

An unknown bath gives V=2.95 mVV=2.95\ \text{mV}. Determine the temperature of the bath in kelvin.

[3]
B

Explain why a temperature change of 15 ∘C15\ ^\circ\text{C} corresponds to a temperature change of 15 K15\ \text{K}, but a temperature of 15 ∘C15\ ^\circ\text{C} is not 15 K15\ \text{K}.

[2]
C

Suggest one feature of the calibration data that would reduce confidence in using the thermocouple for interpolation.

[1]
Question 47
HL • Paper 2
Hard
Calculator Permitted
HL • Paper 2
Hard
Calculator Permitted

A laboratory oven has a flat door of area 0.36 m20.36\ \text{m}^2. The door is made of two layers in contact: an inner ceramic layer of thickness 0.012 m0.012\ \text{m} and thermal conductivity 1.5 W m−1 K−11.5\ \text{W m}^{-1}\ \text{K}^{-1}, and an outer insulation layer of thickness 0.040 m0.040\ \text{m} and thermal conductivity 0.060 W m−1 K−10.060\ \text{W m}^{-1}\ \text{K}^{-1}. The inner surface is at 180 ∘C180\ ^\circ\text{C} and the outer surface is at 35 ∘C35\ ^\circ\text{C}.

A cross-section through a two-layer oven door. The inner hot side, ceramic layer, insulation layer and outer cool side are labelled. Thickness arrows show the two layer thicknesses. A heat-flow arrow points normally through both layers from the oven interior to the room.
A

The heat transfer is assumed to be steady and one-dimensional.

I.

Calculate the thermal resistance per unit area, Δxk\dfrac{\Delta x}{k}, of each layer and hence identify which layer has the larger temperature drop.

[3]
II.

Determine the steady rate of thermal energy transfer through the door.

[2]
B

Explain why the temperature gradient is different in the two layers even though the energy transfer rate is the same through both layers.

[2]
C

Evaluate one additional physical process that could make the actual energy loss from the oven different from the value calculated.

[1]
Question 48
HL • Paper 2
Hard
Calculator Permitted
HL • Paper 2
Hard
Calculator Permitted

A small blackened metal plate of area 0.020 m20.020\ \text{m}^2 is in a vacuum chamber. It is heated electrically with constant power 8.0 W8.0\ \text{W}. When thermal equilibrium is reached, the plate temperature is 345 K345\ \text{K}. The surroundings are at 295 K295\ \text{K}. Assume both faces of the plate radiate as black bodies, so the emitting area is 0.040 m20.040\ \text{m}^2. Take σ=5.67×10−8 W m−2 K−4\sigma=5.67\times10^{-8}\ \text{W m}^{-2}\ \text{K}^{-4}.

A blackened flat plate suspended in a vacuum chamber with electrical leads connected to a power supply. Both faces of the plate radiate to the chamber walls. The chamber walls are labelled as cooler surroundings; no convection arrows should be shown.
A

The net radiative power at equilibrium is compared with the electrical input power.

I.

Calculate the power emitted by the plate at 345 K345\ \text{K}.

[2]
II.

Calculate the power absorbed by the plate from the surroundings, treating the surroundings as black-body radiation at 295 K295\ \text{K}.

[2]
III.

Use your answers to (a)(i) and (a)(ii) to determine whether radiation alone can account for the 8.0 W8.0\ \text{W} electrical input.

[1]
B

Discuss two possible reasons for the discrepancy between the calculated net radiative power and the electrical input power.

[2]
C

Explain why convection is not expected to be an important energy-transfer mechanism in this experiment.

[1]

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B.2 Greenhouse effect