IB Physics HL B 2 2 Emissivity Questions

Practise IB Physics HL B.2.2 by analysing emissivity, net radiation and planetary energy balance with Stefan–Boltzmann models.

Exam points

Calculate net radiation from an emitting body inside a warmer or cooler enclosure using emissivity and T⁴.
Derive planetary equilibrium temperature by combining emissivity, albedo and absorbed solar intensity.

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Study B.2.2—Emissivity conceptsOpen the corresponding Concept lesson for explanations, examples and exam connections.

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The diagram shows a simplified energy-balance model for the Earth surface-atmosphere system.

Figure for Question IB Physics HL B 2 2 Emissivity Questions question 1 — IB Physics HL

The following data are given:

\begin{aligned} \text { Average albedo of Earth } & =0.30 \\ \text { Average global temperature of the surface } & =288 \mathrm{~K} \\ \text { Average Earth-Sun distance } & =1.5 \times 10^{11} \mathrm{~m} \end{aligned}

Determine the average intensity re-radiated by the atmosphere towards the surface. Assume that the emissivity of the surface is 0.90 .

Emitted intensity $=\ll 5.67 \times 10^{-8} \times 0.90 \times 288^{4}=>351 \mathrm{~W} \mathrm{~m}^{-2}$

Intensity leaving Earth $=238 \mathrm{~W} \mathrm{~m}^{-2}$

Re-radiated intensity $=\ll 351-238=>113 \mathrm{~W} \mathrm{~m}^{-2}$

Marking guidance:

Ignore units as they are not required for the answer.

The steps in the calculation must be checked.

Accept outgoing intensity $=240 \mathrm{~W} \mathrm{~m}^{-2}$ for MP2.

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IB Physics HL B 2 2 Emissivity Questions question 1