Nuclear energyAQA A-Level Physics: Topic test

20 questions, 54 marks

AQA A-Level Physics

Nuclear energy topic test

Total 54 marks

Name

Class

Date

1
A student is studying how mass and energy are related, using examples from the Sun and from a light nucleus. Use c = 3.00×10⁸ m s⁻¹, 1 u = 931.5 MeV where required.
(a)
The Sun radiates energy at a power of 3.8×10²⁶ W. At what rate does the Sun lose mass?
[1 mark]
A4.2×10⁹ kg s⁻¹
B1.3×10¹⁸ kg s⁻¹
C3.4×10⁴³ kg s⁻¹
D2.1×10⁹ kg s⁻¹
(b)
Which statement defines the binding energy of a nucleus?
[1 mark]
Athe energy released when the nucleus undergoes radioactive decay
Bthe kinetic energy of the nucleons inside the nucleus
Cthe minimum energy needed to separate the nucleus into its individual nucleons
Dthe energy equivalent of the whole mass of the nucleus
(c)
The mass defect of a lithium-7 nucleus is 0.0421 u. Calculate its binding energy in MeV and its average binding energy per nucleon.
[2 marks]
Total for question 1: 4 marks
2
The nucleus of nitrogen-14 contains 7 protons and 7 neutrons. Its mass is 13.99923 u. The mass of a proton is 1.00728 u and the mass of a neutron is 1.00867 u. Use 1 u = 931.5 MeV.
(a)
What is the mass defect of the nitrogen-14 nucleus?
[1 mark]
A14.112 u
B0.1124 u
C0.0008 u
D0.0161 u
(b)
What is the binding energy of the nitrogen-14 nucleus?
[1 mark]
A15 MeV
B1.2×10⁻⁴ MeV
C0.1124 MeV
D105 MeV
(c)
Calculate the average binding energy per nucleon of nitrogen-14, in MeV.
[2 marks]
Total for question 2: 4 marks
3
In one fission of a uranium-235 nucleus induced by a thermal neutron, the total mass of the particles after the fission is 0.200 u less than the total mass before it. On average 2.4 neutrons are released in each fission. Use 1 u = 931.5 MeV and 1 MeV = 1.60×10⁻¹³ J.
(a)
Calculate the energy released in one fission, in joules.
[3 marks]
(b)
Explain how a steady chain reaction is achieved in a thermal reactor, referring to the neutrons released, the moderator and the control rods.
[4 marks]
Total for question 3: 7 marks
4
A thermal reactor uses fuel rods of enriched uranium-235, heavy water (deuterium oxide) as the moderator, cadmium control rods and a liquid coolant circulating through the core.
(a)
Explain how the moderator slows neutrons and why deuterium nuclei are much better at doing this than lead nuclei would be.
[6 marks]
(b)
The control rods are fully inserted in an emergency shutdown. Explain why the coolant must still circulate afterwards, and describe how the spent fuel is then dealt with safely.
[6 marks]
Total for question 4: 12 marks
5
Two deuterium nuclei fuse: ²₁H + ²₁H → ³₂He + ¹₀n. The nuclear masses are ²₁H 2.01355 u, ³₂He 3.01493 u and ¹₀n 1.00867 u. Use 1 u = 931.5 MeV.
(a)
What is the energy released in this reaction?
[1 mark]
A3.5×10⁻³ MeV
B3.8×10⁻⁶ MeV
C6.5 MeV
D3.3 MeV
(b)
Why must the deuterium nuclei be at a very high temperature for fusion to occur?
[1 mark]
AThey need enough kinetic energy to overcome their electrostatic repulsion and get close enough for the strong interaction to act.
BThey need to be split into protons and neutrons first.
CA high temperature increases the mass of the nuclei, so the mass defect is larger.
DThey need to be slowed down so that neutrons can be absorbed.
(c)
Explain, in terms of binding energy per nucleon, why this reaction releases energy.
[2 marks]
Total for question 5: 4 marks
6
A research reactor uses water as both the moderator and the coolant, and cadmium control rods.
(a)
Which property is the most important for the material of the control rods?
[1 mark]
AIt has nuclei with a mass similar to that of a neutron.
BIt absorbs neutrons readily.
CIt has a very high specific heat capacity.
DIt emits neutrons when struck by neutrons.
(b)
A simple model of moderation uses a moving ball colliding elastically head-on with a stationary ball. For which stationary ball is the transfer of kinetic energy greatest?
[1 mark]
Aa ball much heavier than the moving ball
Ba ball much lighter than the moving ball
Ca ball of the same mass as the moving ball
Da ball of twice the mass of the moving ball
(c)
Explain what is meant by critical mass.
[2 marks]
Total for question 6: 4 marks
7
A research reactor produces a thermal power of 20 MW. Each fission of a uranium-235 nucleus releases 190 MeV. Use 1 MeV = 1.60×10⁻¹³ J, and take the mass of a uranium-235 nucleus to be 235 u, with 1 u = 1.66×10⁻²⁷ kg.
(a)
Calculate the number of fissions per second in the reactor.
[3 marks]
(b)
Calculate the mass of uranium-235 that undergoes fission in one day. State, with a reason, how the spent fuel must be handled.
[4 marks]
Total for question 7: 7 marks
8
The average binding energy per nucleon is 7.6 MeV for uranium-236 and about 8.5 MeV for the two fragments formed when it splits in a fission. The curve of binding energy per nucleon against nucleon number has its peak near iron-56, at 8.8 MeV. A report states that fully fissioning 1.0 kg of uranium-235 releases 8.2×10¹³ J, whereas burning 1.0 kg of natural gas releases 5.5×10⁷ J.
(a)
Estimate the energy released when a uranium-236 nucleus splits into fragments. Explain, using the binding energy per nucleon curve, why the fission of heavy nuclei and the fusion of light nuclei both release energy.
[6 marks]
(b)
Evaluate whether nuclear fission is a better source than natural gas for generating electricity on a large scale.
[6 marks]
Total for question 8: 12 marks

End of questions

Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).