IB Physics SL E.5 Fusion and stars questions

Exam-style multiple choice and written questions with full markschemes. Check multiple choice answers straight away, or type, photograph or draw a written answer and get it marked.

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Multiple choice Written

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Question 1

Multiple choiceMedium1 mark

An HR diagram for stars P and Q is shown. Their unequal stellar parallaxes, measured in arc-seconds, are $p_P$ and $p_Q$ respectively. Which expression gives $d_{\text{red giant}}/d_{\text{white dwarf}}$

Show answer and explanation

Answer: C. On the HR diagram, P is cool and luminous, so it is a red giant; Q is hot and faint, so it is a white dwarf. Using $d\text{ (pc)}=1/p\text{ (arc-second)}$

\frac{d_{\text{red giant}}}{d_{\text{white dwarf}}} =\frac{1/p_P}{1/p_Q} =\frac{p_Q}{p_P}.

A: Uses the parallax ratio directly, as though distance were proportional to parallax.
B: Reverses the required ratio and adds an unnecessary square.
D: Squares the correct inverse-parallax ratio.

Remember: distance and parallax are inversely proportional.

Question 2

Paper 2Medium7 marks

In the core of a young star, deuterium nuclei fuse with protons according to

{}^{2}_{1}\mathrm{H}+{}^{1}_{1}\mathrm{H}\rightarrow{}^{3}_{2}\mathrm{He}+\gamma .

Figure 1 shows the binding energy per nucleon for the nuclei relevant to this reaction. The plotted values are approximate.

Use $1\ \mathrm{MeV}=1.60\times10^{-13}\ \mathrm{J}$

(a)

Use Figure 1 to determine the energy released per reaction. Give your answer in MeV to two significant figures.

[3]

(b)

At a particular stage, this reaction occurs at a rate of $2.0\times10^{37}\ \mathrm{s^{-1}}$ Calculate the energy released per second by these reactions. Give your answer in W to two significant figures.

[2]

(c)

The reaction rate then falls to half its value in (b), while the energy released per reaction remains unchanged. Determine the new energy released per second and explain how it compares with your answer to (b).

[2]

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