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IB Physics SL B 1 Thermal Energy Transfers Questions

Explore how particle models explain temperature and internal energy, how thermal energy moves or changes state, and how radiation links to stellar brightness and temperature.

Syllabus
First assessment 2025
Course
Physics SL
Level
SL

Exam points

  • Use molecular models to explain states, density and internal energy.
  • Convert Celsius and kelvin temperatures; link kelvin temperature to mean particle kinetic energy.
  • Identify thermal-transfer direction and explain energy changes during phase changes.
  • Use Q=mcΔT and Q=mL for heating, cooling and phase changes, including staged energy calculations.
  • Explain conduction, convection and radiation; calculate conduction rate from conductivity, area, thickness and ΔT.
  • Use black-body power and b=L/(4πd²) to relate luminosity, apparent brightness and distance.
  • Apply Wien’s law, λmaxT=2.9×10−3 m K, to infer temperature or peak wavelength.

Covered syllabus points

B.1.1—Molecular statesB.1.2—DensityB.1.3—Temperature scalesB.1.4—Temperature scale changesB.1.5—Kelvin temperature and kinetic energyB.1.6—Internal energyB.1.7—Thermal transfer directionB.1.8—Phase changeB.1.9—Specific heat and latent heatB.1.10—Thermal transfer mechanismsB.1.11—ConductionB.1.12—Conduction rateB.1.13—ConvectionB.1.14—Black-body radiationB.1.15—Apparent brightnessB.1.16—Luminosity and brightnessB.1.17—Wien’s displacement law

Question 1

[Maximum number: 10]

A cylindrical cork of height H and cross-sectional area A is floating stationary in water. Its depth below the water surface is D.

Figure for Question 1 — IB Physics SL

Question (a)

(a)

Explain why the density of most substances in a solid state is larger than its density in a liquid state.

Water shows an anomaly with respect to what is stated in (c)(i).
Graph 1 shows the variation with temperature of the density of water between −100∘C-100^{\circ} \mathrm{C} and 100∘C100^{\circ} \mathrm{C}. Graph 2 shows the same graph enlarged for the range 0 to 10∘C10^{\circ} \mathrm{C}.

[ 2 ]

Question (b)

(b)

On a winter day, the surface of a lake is frozen. The temperature of the air above the lake is −6.0∘C-6.0^{\circ} \mathrm{C}. The layer of ice frozen on the surface of the lake has a thickness of 1.9 cm .

[ 8 ]

Question (i)

(i)

The thermal conductivity of ice is 2.3Wm−1 K−12.3 \mathrm{Wm}^{-1} \mathrm{~K}^{-1}. Calculate the rate per unit area at which thermal energy leaves the lake by conduction through the ice layer.

[ 2 ]

Question (ii)

(ii)

The depth of water below the ice is 22 m and its average initial temperature is 2.0∘C2.0^{\circ} \mathrm{C}. Estimate the minimum thermal energy per unit area that must be removed to freeze all the water in the lake.

The following data are available:

 Specific heat capacity of water =4.2×103Jkg−1 K−1 Latent heat of fusion of water =3.3×105Jkg−1ρwater =1000 kg m−3\begin{aligned} \text { Specific heat capacity of water } & =4.2 \times 10^{3} \mathrm{Jkg}^{-1} \mathrm{~K}^{-1} \\ \text { Latent heat of fusion of water } & =3.3 \times 10^{5} \mathrm{Jkg}^{-1} \\ \rho_{\text {water }} & =1000 \mathrm{~kg} \mathrm{~m}^{-3} \end{aligned}

Layers of ice on lakes do not grow thicker than a small percentage of the lake's depth even when the exterior temperature remains constant below the freezing point for some time.

[ 3 ]

Question (iii)

(iii)

Explain how the rate per unit area at which thermal energy leaves the lake by conduction through the ice layer changes as the layer of ice grows thicker.

[ 1 ]

Question (iv)

(iv)

Discuss why the anomaly in the value of the density of water supports life in water on Earth.

[ 2 ]

Question 2

[Maximum number: 2]

This question is about a tidal power station.

A tidal power station is built for a coastal town. Sea water is stored in a tidal basin behind a dam at high tide and released in a controlled manner between high tides, so that it passes through turbines to generate electricity.

The following data are available.

Table for Question 2 — IB Physics SL

Show that the mass of sea water released between successive high and low tides is about 2.8×108 kg2.8 \times 10^{8} \mathrm{~kg}.

Question 3

[Maximum number: 1]

Which of the following is equivalent to a temperature of −100∘C-100^{\circ} \mathrm{C} ?

A

-373 K

B

-173 K

C

173 K

D

373 K373 \mathrm{~K}

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