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IB Physics: Fission — Practice Questions & Answers
134 practice questions available for this topic — here are 10 with full answers and explanations.
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Practice questions with answers
1
Multiple choice · Easy
Nuclear fission is the process in which:
- A heavy nucleus splits into smaller nuclei
- Two light nuclei join together
- A nucleus emits a gamma ray only
- An electron is captured by a proton
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WhyIn fission a large, heavy nucleus (such as uranium-235) splits into smaller nuclei, releasing energy and neutrons.
2
Multiple choice · Medium
In a fission reactor, the role of the moderator is to:
- Slow down neutrons
- Absorb all neutrons
- Speed up neutrons
- Cool the turbines
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WhyThe moderator (e.g. water or graphite) slows down fast neutrons so they can efficiently cause further fission.
3
Multiple choice · Medium
The role of control rods in a nuclear reactor is to:
- Absorb neutrons to control the reaction rate
- Slow down neutrons
- Provide fuel for fission
- Generate the electrical output
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WhyControl rods (e.g. boron or cadmium) absorb neutrons, controlling the rate of the chain reaction.
4
Multiple choice · Easy
A self-sustaining series of fission reactions is called a:
- Chain reaction
- Decay series
- Fusion cycle
- Resonance
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WhyA chain reaction occurs when neutrons released by one fission trigger further fissions.
5
Multiple choice · Hard
The energy released in fission comes from a small loss of mass, related to energy by:
- $E=mc^{2}$
- $E=\frac{1}{2}mv^{2}$
- $E=mgh$
- $E=mc$
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WhyEinstein's mass-energy equivalence $E=mc^{2}$ converts the mass defect into the released energy.
6
Multiple choice · Medium
Fission is typically triggered when a uranium-235 nucleus absorbs a:
- Neutron
- Proton
- Electron
- Gamma photon
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WhyU-235 undergoes fission when it absorbs a (slow) neutron, becoming unstable and splitting.
7
Fill in the blank · Easy
In a reactor, the rods that absorb neutrons to regulate the reaction are called control .
Answer:
rods
WhyControl rods made of neutron-absorbing material are inserted or withdrawn to adjust the reaction rate.
8
Fill in the blank · Medium
The energy released by the mass defect in fission is given by Einstein's equation $E=mc^{}$.
Answer:
2
Why$E=mc^{2}$ relates the lost mass to the released energy, with $c$ the speed of light.
9
Multiple choice · Medium
Which reactor component slows down neutrons to increase the chance of further fission?
- The moderator
- The control rods
- The fuel rods
- The heat exchanger
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WhyThe moderator slows fast neutrons so they are more readily absorbed by fissile nuclei.
10
Multiple choice · Medium
What is the role of the control rods in a fission reactor?
- They absorb neutrons to control the reaction
- They slow the neutrons down
- They provide the fissile fuel
- They transfer heat to water
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WhyThey absorb neutrons to control the rate of the chain reaction.
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