# Exam-style Questions: Nuclear Energy

Energy released is as a result of the mass defect. Some mass is turned into pure energy. The conversion is calculated by:

E = mc2

So to find out the energy released or absorbed you need to find out how much mass is lost or gained in the reaction and then put that figure in the equation above.

The change in mass is found by doing:

mN + mHe - mO - mH i.e. the mass of the left side minus the mass of the right side.

The energy is found by multiplying this by c2. Hence, answer C.

1. In the equation:

which of the following gives the value of energy released or absorbed by the reaction?

Take:

mN as the mass of N-14

mHe as the mass of He-4

mO as the mass of O-17

mH as the mass of H-1

• (mN + mHe + mO + mH).c2
• (mN + mHe - mO + mH).c2
• (mN + mHe - mO - mH).c2
• (mN + mHe - mO - mH) / c2
2. Give 2 arguments for and against nuclear power.

(Marks available: 4)

Answer outline and marking scheme for question: 1

Advantages: Cheap energy production, conservation of fossil fuels, no harmful gas by-products, production of useful radioactive nuclides

(1 mark for each up to 2)

Disadvantages: Possibility of accidents (explosions, radioactive leaks), produces radioactive waste which is difficult to dispose of, high decommissioning costs

(1 mark for each up to 2)

(Marks available: 4)

3. The mass defect of a carbon -12 nucleus is found to be -0.0989u.

Calculate:

a) The binding energy of the a carbon - 12 nucleus in joules

b) The binding energy per nucleon in MeV

Take:

u to be 1.66056 x 10 -27 kg;

c to be 3.0 x 10 8 ms-1;

e to be 1.602 x 10 -19 C

(Marks available: 4)

Answer outline and marking scheme for question: 2

a) -1.478 x 10 -11 J

(2 marks)

b) 92.26 MeV

(2 marks)

(Marks available: 4)

4. In a nuclear power station a controlled nuclear chain-reaction is used to produce energy. Control rods and a moderator are used to ensure that the nuclear reactions proceed at the correct rate.

a) With the help of a sketch explain what a chain-reaction is

b) What role does the moderator play in a nuclear reactor, why is it important and suggest a suitable material.

(Marks available: 6)

Answer outline and marking scheme for question: 3

a) Neutron strikes nucleus causing it to split into fragments (1 mark) Neutrons are released (1 mark) Released neutrons cause further fissions (1 mark)

b) The moderator slows fast moving neutrons (1 mark) so that they have more chance of causing fission when they strike nuclei (1 mark) Suitable materials are graphite and water (1 mark)

(Marks available: 6)

5. Explain in terms of binding energy why very large nuclides undergo fission.

(Marks available: 2)

Answer outline and marking scheme for question: 4

Iron nucleus has the lowest binding energy per nucleon. (1 mark) By breaking into smaller nuclei closer in size to the iron nucleus, large nuclei reduce their binding energy and hence become more stable. (1 mark)