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Date May 2021 Marks available 2 Reference code 21M.2.SL.TZ1.4
Level Standard level Paper Paper 2 Time zone 1
Command term Derive Question number 4 Adapted from N/A

Question

A planet orbits at a distance d from a star. The power emitted by the star is P. The total surface area of the planet is A.

Explain why the power incident on the planet is

                                                                P4πd2×A4.

[2]
a.i.

The albedo of the planet is αp. The equilibrium surface temperature of the planet is T. Derive the expression

T=P(1-αp)16πd2eσ4

where e is the emissivity of the planet.

[2]
a.ii.

On average, the Moon is the same distance from the Sun as the Earth. The Moon can be assumed to have an emissivity e = 1 and an albedo αM = 0.13. The solar constant is 1.36 × 103 W m−2. Calculate the surface temperature of the Moon.

[2]
b.

Markscheme

P4πd2 is the power received by the planet/at a distance d «from star» 

A4 is the projected area/cross sectional area of the planet 

 

a.i.

use of eσAT4 OR P4πd2×A4×(1-αp) 

with correct manipulation to show the result

 

a.ii.

1.36×103×0.874×5.67×10-84 

T = 268.75 «K» ≅ 270 «K»

b.

Examiners report

[N/A]
a.i.
[N/A]
a.ii.
[N/A]
b.

Syllabus sections

Core » Topic 8: Energy production » 8.2 – Thermal energy transfer
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