Fig. 1 shows the nuclei used in a common fusion reaction. Deuterium has one proton and one neutron. Tritium has one proton and two neutrons. When they fuse,...
Question 1 Report
Fig. 1 shows the nuclei used in a common fusion reaction. Deuterium has one proton and one neutron. Tritium has one proton and two neutrons. When they fuse, a helium nucleus and a neutron are produced. Reactor designers prefer this reaction because it can occur at lower temperatures than many other fusion reactions.
(a) What is the proton number of the helium nucleus shown? [1]
(b) Complete the statement: the neutron has no __________ charge. [1]
(c) Describe how nucleon number is conserved in the reaction. [2]
(d) Give one reason why the released neutron is difficult to confine using the magnetic field. [1]
Fig. 1 shows two forces acting on material near the surface of a star. Gravity pulls the material inward. Energy from nuclear fusion causes pressure that pushes outward. Astronomers use this model when comparing ordinary stars with stars that have used most of their hydrogen fuel. The arrows are not to scale.
(a) Describe the condition shown by the two equal arrows. [1]
(b) Explain what happens to the fusion rate if the core becomes slightly hotter. [2]
(c) Give one change that can occur when a star has very little hydrogen remaining in its core. [2]
Answer Details
First question set
- (a) The helium nucleus is \(^{4}_{2}\mathrm{He}\), so its proton number is 2. [1]
- (b) A neutron has no electric charge. [1]
- (c) Nucleon number is conserved:
\[2+3=5\text{ nucleons before}\]
\[4+1=5\text{ nucleons after}\]
There are therefore five nucleons on each side of the reaction. [2] - (d) A neutron has no electric charge, so a magnetic field does not deflect or confine it. [1]
Second question set
- (a) The equal opposite arrows show balanced forces, or equilibrium. [1]
- (b) If the core becomes hotter, nuclei move faster. Collisions, and therefore fusion reactions, occur more often. [2]
- (c) As hydrogen becomes scarce, the core can contract and its temperature can rise. The outer layers may expand so the star becomes a red giant, and helium fusion may begin. Any two linked valid changes gain full credit. [2]
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