IB Physics HL E.5.7 Stellar radii Question Bank

Practise IB Physics SL/HL E.5.7 by applying stellar radii concepts to exam-style physics questions.

Exam points

identify the relevant physical quantity, model or diagram
apply the correct equation and units to the evidence
justify the result using conservation laws, fields or energy relationships

[Maximum number: 4]

Alpha Centauri A and B is a binary star system in the main sequence.

Table for Question E.5.7—Stellar radii question 1 — IB Physics HL

(a)

The luminosity of the Sun is $3.8 \times 10^{26} \mathrm{~W}$ . Calculate the radius of Alpha Centauri A.

[ 2 ]

$\begin{aligned} r=\sqrt{\frac{1.5 \times 3.8 \times 10^{26}}{5.67 \times 10^{-8} \times 4 \pi \times 5800^{4}}} =8.4 \times 10^{8}<\mathrm{m} \gg \end{aligned}$

Award [2] for a bald correct answer.

(b)

Show, without calculation, that the radius of Alpha Centauri B is smaller than the radius of Alpha Centauri A.

[ 2 ]

« $A=\frac{L}{\sigma T^{4}}$ » B and A have similar temperatures

so areas are in ratio of luminosities

«so B radius is less than A»

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E.5.7—Stellar radii question 1

Question (a)

Question (b)