IB Physics HL B 1 16 Luminosity and Brightness Questions

Practise IB Physics HL B.1.16 by linking luminosity, apparent brightness, magnitude and distance methods such as standard candles and Cepheids.

Exam points

Apply b = L/(4πd²) to relate apparent brightness to luminosity and distance.
Calculate luminosity, distance or apparent brightness with inverse-square reasoning and consistent units using complete evidence.

[Maximum number: 2]

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

Figure for Question IB Physics HL B 1 16 Luminosity and Brightness 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}

Show, with reference to the solar constant, that the total power radiated by the Sun is about $4 \times 10^{26} \mathrm{~W}$ .

Recognition that $r=1.5 \times 10^{11} m$ AND $S=1.36 \times 10^{3} \mathrm{~W} \mathrm{~m}^{-2}$ $4 \pi\left(1.5 \times 10^{11}\right)^{2} \times 1.36 \times 10^{3}$ or $3.8 \times 10^{26} \mathrm{~W}$

Unit is not required.

The values of r and S must be seen to award MP1.

Marking guidance:

Allow ECF from use of
$S=1.4 \times 10^{3} \mathrm{Wm}^{-2}$

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IB Physics HL B 1 16 Luminosity and Brightness Questions question 1