AP Physics 2 Quiz: Fission Fusion And Nuclear Decay

What this quiz covers

This quiz focuses on Fission Fusion And Nuclear Decay, giving you a quick way to practice the rules, question types, and explanations that matter most for AP Physics 2.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

Question 1

1. Fusion, because two nuclei combine into a heavier nucleus after overcoming electrostatic repulsion. (correct answer)
2. Fission, because a heavy nucleus splits into two medium nuclei and releases chemical energy.
3. Alpha decay, because the nucleus spontaneously emits $^{4}\mathrm{He}$ without any collision.
4. Gamma decay, because only a photon is emitted and the nucleus composition changes.

Explanation: This question tests understanding of fission, fusion, and nuclear decay. When nitrogen-14 absorbs an alpha particle (helium-4), the nuclei combine to form a heavier nucleus, which is the defining characteristic of fusion. The reaction produces oxygen-17 plus a proton, conserving both mass number (14+4=17+1) and atomic number (7+2=8+1). Fusion requires overcoming the electrostatic repulsion between positively charged nuclei, which is why bombardment experiments use high-energy particles. Choice C incorrectly calls this alpha decay, which is emission rather than absorption of an alpha particle. The key insight is that fusion involves combining nuclei, not splitting or emitting particles.

Question 2

1. Energy is released because fusion requires no high temperature and occurs when nuclei move slowly.
2. Energy is released because the protons create stronger chemical bonds when they form helium atoms.
3. Energy is released because mass is conserved exactly, so no energy conversion is needed.
4. Energy is released because helium's mass is slightly less than the initial protons, and $\Delta mc^2$ is released. (correct answer)

Explanation: This question tests understanding of fission, fusion, and nuclear decay. In stellar fusion, four hydrogen nuclei (protons) ultimately combine through a series of reactions to form one helium-4 nucleus, releasing tremendous energy. The helium nucleus has significantly less mass than four separate protons, and this mass defect is converted directly to energy according to Einstein's equation E=mc². This occurs because helium-4 has much greater binding energy per nucleon than individual protons, representing a more stable nuclear configuration where nucleons are bound more tightly. Choice C incorrectly claims mass is conserved exactly, missing the fundamental principle that nuclear energy comes from mass-energy conversion. To understand fusion energy, remember that nuclear energy comes from changes in binding energy, with the mass defect converting to released energy.

Question 3

1. The mass number decreases by 4 and the atomic number decreases by 2.
2. The atomic number decreases by 1 while the mass number stays the same. (correct answer)
3. The nucleus releases energy because electrons drop to lower orbitals and emit light.
4. The atomic number increases by 1 while the mass number stays the same.

Explanation: This question tests understanding of fission, fusion, and nuclear decay. Beta-plus (β⁺) decay occurs when a proton in the nucleus converts to a neutron, emitting a positron and neutrino. This decreases the atomic number by 1 (from 11 for sodium to 10 for neon) while the mass number remains constant at 22. The energy released comes from mass-energy equivalence: the slight mass difference between initial and final nuclear states is converted to kinetic energy of the emitted particles. Choice D incorrectly attributes energy to electron orbital transitions (a misconception confusing nuclear decay with atomic processes). The key is that nuclear decay changes the nucleus composition through binding energy changes.

Question 4

1. High temperature provides kinetic energy to overcome electrostatic repulsion so nuclei can get close enough to fuse. (correct answer)
2. High temperature is needed so electrons can form stronger chemical bonds that drive the reaction.
3. High temperature ensures the total mass is conserved exactly, which causes energy to appear.
4. High temperature is unnecessary because fusion happens readily at room temperature when pressure is low.

Explanation: This question tests understanding of fission, fusion, and nuclear decay. Fusion requires extremely high temperatures because the positively charged nuclei must overcome their strong electrostatic repulsion to get close enough for the strong nuclear force to bind them. At high temperatures, nuclei have sufficient kinetic energy to approach within about 10⁻¹⁵ meters where nuclear forces dominate. The energy released comes from the mass defect when lighter nuclei form a more tightly bound heavier nucleus, converting mass to energy via E=mc². Choice B incorrectly attributes fusion to chemical bonding, which involves only electrons, not nuclear processes. Remember that fusion requires overcoming Coulomb repulsion between positive nuclei, which demands extreme temperatures like those in stellar cores.

Question 5

1. Fusion combines light nuclei and requires overcoming Coulomb repulsion, whereas fission splits heavy nuclei after neutron absorption. (correct answer)
2. Fusion splits heavy nuclei into lighter ones, whereas fission combines light nuclei into heavier ones.
3. Fusion is a chemical process involving electrons, whereas fission is a chemical process involving ions.
4. Fusion occurs easily at low temperatures, whereas fission requires extremely high temperatures to start.

Explanation: This question tests understanding of fission, fusion, and nuclear decay. Fusion in stars combines light nuclei (like hydrogen) into heavier ones (like helium), requiring extreme temperatures to overcome Coulomb repulsion between positive nuclei. Fission in reactors splits heavy nuclei (like uranium) into lighter fragments, typically initiated by neutron absorption at relatively low temperatures. Both processes release energy through mass-energy conversion when products have higher binding energy per nucleon than reactants. Choice B reverses the definitions, incorrectly stating fusion splits and fission combines. Remember the distinction: fusion fuses light nuclei at high temperatures, while fission splits heavy nuclei often triggered by thermal neutrons.

Question 6

1. Its mass number decreases by 4 and its atomic number decreases by 2. (correct answer)
2. Its mass number decreases by 2 and its atomic number decreases by 4.
3. Its mass number increases by 4 and its atomic number increases by 2.
4. Its mass number stays the same and its atomic number increases by 1.

Explanation: This question tests understanding of fission, fusion, and nuclear decay. Alpha decay occurs when a nucleus emits an alpha particle (helium-4 nucleus), which contains 2 protons and 2 neutrons. This emission decreases the parent nucleus's mass number by 4 (total nucleons lost) and atomic number by 2 (protons lost), as seen when uranium-238 becomes thorium-234. The energy for this decay comes from the mass difference between the parent nucleus and the combined mass of the daughter nucleus plus alpha particle. Choice A reverses the changes to mass number and atomic number, a common error when students confuse which number represents what. Remember that in alpha decay, the mass number drops by 4 and atomic number drops by 2, following the composition of the emitted helium nucleus.

Question 7

1. High temperature provides kinetic energy to overcome electrostatic repulsion so the strong force can bind the nuclei. (correct answer)
2. High temperature is needed to break chemical bonds so nuclei can share electrons and fuse.
3. High temperature is required because mass must be conserved exactly, preventing any energy release at low temperature.
4. High temperature is unnecessary because fusion of hydrogen isotopes occurs efficiently at room temperature.

Explanation: This question tests understanding of fission, fusion, and nuclear decay. Fusion of light nuclei requires extremely high temperatures because the positively charged nuclei must overcome their strong electrostatic repulsion to get close enough for the strong nuclear force to bind them. At high temperatures, nuclei have sufficient kinetic energy to approach within about 10^-15 meters, where the attractive strong force overcomes electrostatic repulsion. The fusion of deuterium and tritium releases energy because helium-4 has higher binding energy per nucleon than the reactants, converting mass to energy via E=mc². Choice B incorrectly invokes chemical bonds, which are irrelevant to nuclear processes. The key principle is that fusion requires overcoming Coulomb repulsion through high kinetic energy.

Question 8

1. A photon that carries chemical energy, leaving atomic number and mass number unchanged.
2. An electron from the nucleus, increasing atomic number by 1 while mass number stays the same.
3. A neutron that triggers fusion at low temperature, increasing both atomic and mass numbers.
4. A helium nucleus with 2 protons and 2 neutrons, reducing atomic number by 2 and mass number by 4. (correct answer)

Explanation: This question tests understanding of fission, fusion, and nuclear decay. An alpha particle is a helium-4 nucleus consisting of 2 protons and 2 neutrons, which explains why uranium-238 (92 protons) becomes thorium-234 (90 protons) after alpha emission. The mass number decreases by 4 (from 238 to 234) because the alpha particle carries away 2 protons and 2 neutrons. Alpha decay occurs in heavy nuclei that have too many protons and neutrons, and emitting an alpha particle helps the nucleus move toward stability. Choice B incorrectly describes beta decay, confusing the type of particle emitted. The key is recognizing that alpha particles are helium nuclei that reduce both atomic and mass numbers.

Question 9

1. The reaction releases chemical bond energy when uranium atoms rearrange their electron shells.
2. Mass is strictly conserved in the reaction, so no energy can be released.
3. The products have greater total binding energy per nucleon, so the mass defect increases and $E=mc^2$ is released. (correct answer)
4. The process is fusion because heavy nuclei combine at low temperature to form heavier nuclei.

Explanation: This question tests understanding of fission, fusion, and nuclear decay. In nuclear fission, a heavy nucleus like U-235 splits into two medium-sized nuclei after absorbing a neutron. The key insight is that the binding energy per nucleon is higher for medium-mass nuclei than for very heavy nuclei, meaning the products are more tightly bound. This increase in binding energy per nucleon corresponds to a greater mass defect (the difference between the mass of separated nucleons and the bound nucleus), and this "missing" mass is converted to energy according to Einstein's equation E=mc². Choice B incorrectly attributes the energy to chemical bonds, which involve electrons rather than nuclear processes. The strategy to remember is that nuclear energy comes from changes in binding energy, with more tightly bound products releasing energy.

Question 10

1. Energy is released because the helium nucleus has greater binding energy per nucleon than the reactants. (correct answer)
2. Energy is released because the neutron forms a chemical bond with helium, lowering electron energy.
3. Energy is released because fusion occurs easily at low temperature when nuclei move slowly.
4. Energy is released because the total mass of products must equal the total mass of reactants exactly.

Explanation: This question tests understanding of fission, fusion, and nuclear decay. In deuterium-tritium fusion, two hydrogen isotopes combine to form helium-4 plus a neutron, releasing tremendous energy. The helium-4 nucleus has much greater binding energy per nucleon than either deuterium or tritium, meaning its nucleons are bound much more tightly. This increase in binding energy per nucleon corresponds to a mass defect—the products have less total mass than the reactants—and this missing mass is converted to kinetic energy of the helium nucleus and neutron. Choice D incorrectly suggests fusion occurs easily at low temperature, when actually it requires extreme conditions to overcome electrostatic repulsion between positive nuclei. When analyzing fusion reactions, remember that nuclear energy comes from changes in binding energy, with products having higher binding energy per nucleon than reactants.

Question 11

1. Energy is released because the products have greater total binding energy, so mass converts to kinetic energy. (correct answer)
2. Energy is released because alpha decay is a type of low-temperature fusion of two heavy nuclei.
3. Energy is released because nucleons are created from energy, increasing total mass.
4. Energy is released because electrons in uranium form stronger chemical bonds after the decay.

Explanation: This question tests understanding of fission, fusion, and nuclear decay. Alpha decay occurs when a heavy nucleus emits an alpha particle (helium-4 nucleus), transforming uranium-238 into thorium-234. Energy is released because the combined binding energy of the thorium nucleus plus the alpha particle exceeds that of the original uranium nucleus. This increase in total binding energy means the products are more stable, and the corresponding mass defect is converted to kinetic energy of the alpha particle and recoiling thorium nucleus. Choice D incorrectly calls alpha decay a type of fusion, when it's actually a decay process that reduces nuclear size rather than combining nuclei. To analyze nuclear reactions correctly, remember that nuclear energy comes from changes in binding energy—products with greater total binding energy have less mass than reactants.

Question 12

1. Energy is released because fusion happens when a heavy nucleus emits an alpha particle at low temperature.
2. Energy is released because total mass is conserved exactly, so no energy conversion occurs.
3. Energy is released because the products have lower total mass, so $\Delta m c^2$ becomes kinetic energy. (correct answer)
4. Energy is released because electron sharing creates stronger chemical bonds in thorium.

Explanation: This question tests understanding of fission, fusion, and nuclear decay. Alpha decay occurs when a heavy nucleus emits an alpha particle (helium-4 nucleus), decreasing its mass number by 4 and atomic number by 2. The energy released comes from mass-energy equivalence: the combined mass of thorium-234 and helium-4 is less than the original uranium-238, and this mass defect (Δm) is converted to kinetic energy via E=Δmc². The products have greater binding energy per nucleon, making them more stable than the parent nucleus. Choice A incorrectly attributes energy to chemical bonding (a misconception confusing nuclear and chemical processes). Remember that nuclear energy comes from changes in binding energy, manifested as mass differences.

Question 13

1. This is fission, because a heavy nucleus splits into lighter nuclei, unlike fusion which combines light nuclei. (correct answer)
2. This is fusion, because it can occur readily at room temperature when atoms collide.
3. This is chemical combustion, because energy comes from rearranging electrons in plutonium compounds.
4. This is fusion, because a heavy nucleus combines with a neutron to form a heavier stable nucleus.

Explanation: This question tests understanding of fission, fusion, and nuclear decay. Nuclear fission occurs when a heavy nucleus like plutonium-239 splits into two medium-mass fragments plus several neutrons, releasing energy because the products have higher binding energy per nucleon than the original heavy nucleus. This contrasts with fusion, where light nuclei combine to form heavier ones, typically occurring with hydrogen isotopes forming helium. The mass of the fission products is less than the original plutonium nucleus, and this mass defect converts to kinetic energy of the fragments and neutrons. Choice A incorrectly calls this fusion and misunderstands that adding a neutron to trigger fission is not the same as fusion combining nuclei. The key distinction is that fission splits heavy nuclei while fusion combines light nuclei, both releasing energy when products have higher binding energy per nucleon.

Question 14

1. Energy is released because the total binding energy of the fission products is greater, so mass decreases and $E=mc^2$. (correct answer)
2. Energy is released because fission requires extremely high temperature to force nuclei together.
3. Energy is released because the products have greater total mass than the reactants.
4. Energy comes primarily from rearranging electron bonds in uranium compounds during the reaction.

Explanation: This question tests understanding of fission, fusion, and nuclear decay. In nuclear fission, a heavy nucleus splits into lighter fragments, and the key to energy release lies in mass-energy equivalence: when the total mass of products is less than the reactants, the missing mass converts to energy via E=mc². The fission products have higher binding energy per nucleon than the original uranium nucleus, meaning they are more tightly bound and have less mass overall. This mass defect becomes the kinetic energy of the fragments and radiation. Choice A incorrectly attributes energy to chemical electron bonds rather than nuclear binding energy, confusing atomic-scale with nuclear-scale processes. The strategy to remember is that nuclear energy comes from changes in binding energy, where more tightly bound products mean mass converts to energy.

Question 15

1. Energy comes from the difference in nuclear binding energy, with a mass defect converted to energy. (correct answer)
2. Energy comes mainly from chemical bond rearrangements among the fission fragments.
3. Energy comes from increased total rest mass of products compared with reactants.
4. Energy comes because nucleons are created from nothing, increasing mass and releasing energy.

Explanation: This question tests understanding of fission, fusion, and nuclear decay. In nuclear fission, the energy released comes from the difference in nuclear binding energy between reactants and products. The fission fragments have greater binding energy per nucleon than uranium-235, meaning they are more tightly bound and stable. This increased binding energy manifests as a mass defect - the products have less total mass than the reactants, and this missing mass is converted to energy via E=mc². Choice B incorrectly states products have increased mass (a misconception reversing the mass-energy relationship). Remember that nuclear energy comes from changes in binding energy, always resulting in lower total mass for energy-releasing reactions.

Question 16

1. Only the nuclear energy level decreases while mass number and atomic number stay the same. (correct answer)
2. Only the electron configuration changes while the nucleus remains unchanged.
3. The mass number decreases by 4 and the atomic number decreases by 2.
4. The atomic number increases by 1 while the mass number stays the same.

Explanation: This question tests understanding of fission, fusion, and nuclear decay. Gamma decay occurs when an excited nucleus (Co-60*) releases energy by emitting a high-energy photon without changing its composition - the mass number and atomic number remain the same. The energy comes from the nucleus transitioning from a higher to lower energy state, with the energy difference carried away by the gamma ray according to E=hf. This is pure energy emission with no change in nucleon number or arrangement. Choice D incorrectly suggests only electron configuration changes (a misconception confusing nuclear and atomic processes). The strategy is that nuclear energy comes from changes in binding energy, and gamma emission represents energy release without composition change.

Question 17

1. It decreases the mass number by 4 and the atomic number by 2.
2. It increases the atomic number by 1 by converting a neutron into a proton.
3. It changes the nucleus from an excited state to a lower-energy state without changing $A$ or $Z$. (correct answer)
4. It occurs when two light nuclei combine at low temperature due to electron bonding.

Explanation: This question tests understanding of fission, fusion, and nuclear decay. Gamma emission occurs when an excited nucleus transitions to a lower energy state by emitting a high-energy photon, without changing either the mass number or atomic number of the nucleus. This often follows other decay processes that leave the nucleus in an excited state, and the gamma ray carries away the excess energy as the nucleus settles into a more stable configuration. The energy comes from the difference between nuclear energy levels, analogous to electron transitions but at much higher energies. Choice B incorrectly describes beta decay, which would change the atomic number by converting a neutron to a proton. Remember that gamma emission is pure energy release without particle emission, preserving both A and Z while the nucleus drops to a lower energy state.

Question 18

1. High temperature is needed because heavy nuclei split more easily when heated.
2. High temperature is needed to overcome electrostatic repulsion between positively charged nuclei. (correct answer)
3. High temperature is needed to break chemical bonds so nuclei can stick together.
4. High temperature is needed because fusion only occurs after electrons are removed from atoms.

Explanation: This question tests understanding of fission, fusion, and nuclear decay. Fusion requires extremely high temperatures because the positively charged nuclei must overcome their strong electrostatic repulsion to get close enough for the strong nuclear force to bind them. At high temperatures, nuclei have sufficient kinetic energy to overcome this Coulomb barrier. Once fused, the helium nucleus has greater binding energy per nucleon than the hydrogen isotopes, and the mass defect is converted to energy via E=mc². Choice B incorrectly suggests breaking chemical bonds (a misconception confusing nuclear fusion requirements with chemical reactions). Remember that nuclear energy comes from changes in binding energy, but fusion requires overcoming electrostatic repulsion first.

Question 19

1. Energy is released because chemical bonds form between barium and krypton atoms.
2. Energy is released because some mass becomes energy as products have greater binding energy per nucleon. (correct answer)
3. Energy is released because total mass is exactly conserved with no conversion to other forms.
4. Energy is released because fusion occurs at low temperature when heavy nuclei split into lighter ones.

Explanation: This question tests understanding of fission, fusion, and nuclear decay. In nuclear fission, a heavy nucleus like uranium-235 absorbs a neutron and splits into lighter nuclei (barium and krypton), releasing additional neutrons and energy. The energy comes from mass-energy equivalence: the total mass of the products is slightly less than the reactants, and this missing mass (mass defect) is converted to energy according to E=mc². The products have greater binding energy per nucleon than the original uranium nucleus, meaning they are more stable and the excess binding energy is released. Choice A incorrectly suggests chemical bonding (a misconception that confuses nuclear and chemical processes). The key strategy is that nuclear energy comes from changes in binding energy, not from chemical bonds or electron rearrangements.

Question 20

1. Using fuel so hot that nuclei overcome repulsion and fuse more often.
2. Ensuring enough fissile nuclei so, on average, at least one emitted neutron causes another fission. (correct answer)
3. Increasing electron sharing between atoms so chemical reactions release more energy.
4. Preventing any mass defect so energy cannot be released as radiation or kinetic energy.

Explanation: This question tests understanding of fission, fusion, and nuclear decay. A nuclear chain reaction sustains itself when each fission event produces neutrons that trigger additional fissions, requiring a critical mass of fissile material where at least one neutron per fission causes another fission on average. The key is maintaining the neutron multiplication factor at or above 1, which depends on having sufficient fissile nuclei density and proper neutron moderation. Energy release comes from the mass defect when heavy nuclei split into lighter fragments with higher total binding energy. Choice C incorrectly focuses on chemical electron sharing rather than nuclear processes, confusing atomic bonding with nuclear reactions. The strategy for chain reactions is ensuring neutron economy: enough fissile material so emitted neutrons cause further fissions rather than escaping or being absorbed without fission.