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

Identify forces as interactions between bodies, specifying the two interacting bodies and the force direction.
Represent interaction pairs and distinguish contact from non-contact forces using complete diagrams and mark-scheme evidence.

[Maximum number: 3]

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