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Physics Chapter 14 : Topic 1
Conservation of Nucleon Number and Charge
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In a nuclear reaction, the quantity that must always remain conserved is:
Reasoning: Nuclear processes obey conservation laws; total nucleon number and total charge remain constant before and after the reaction.
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The nucleon number of an atom represents the total number of:
Reasoning: Nucleon number (mass number $\mathbf{A}$) is the sum of protons and neutrons in the nucleus.
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In a nuclear equation, the sum of mass numbers before and after the reaction must be:
Reasoning: Nucleon number is conserved, so total nucleons remain unchanged.
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Which conservation law ensures that the total number of protons remains unchanged in a nuclear reaction?
Reasoning: Each proton has a positive charge, so conservation of charge ensures total proton charge remains constant.
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In the nuclear reaction: $\mathbf{\ }_{\mathbf{7}}^{\mathbf{14}}\mathbf{N +}\mathbf{\ }_{\mathbf{2}}^{\mathbf{4}}\mathbf{He\ \ }\overset{\mathbf{\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ }}{\rightarrow}\mathbf{\ }\mathbf{\ }_{\mathbf{8}}^{\mathbf{17}}\mathbf{O + X}$ The unknown particle $\mathbf{X}$ is:
Reasoning: Nucleon numbers:$\mathbf{14 + 4 = 18}$, oxygen has $\mathbf{17}$, so $\mathbf{X}$ has nucleon number $\mathbf{1}$. Charge: $\mathbf{7 + 2 = 9}$, oxygen has charge $\mathbf{8}$, so $\mathbf{X}$ has charge $\mathbf{0\ }\overset{\ \ \ \ \ \ \ \ \ \ \ }{\rightarrow}$ neutron.
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Which statement about nuclear reactions is correct?
Reasoning: Nuclear reactions rearrange nucleons but do not create or destroy total nucleon number.
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During alpha decay, the nucleus emits:
Reasoning: An alpha particle is a helium nucleus containing $\mathbf{2}$ protons and $\mathbf{2}$ neutrons.
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When a nucleus undergoes alpha decay, its nucleon number changes by:
Reasoning: An alpha particle contains four nucleons, so the parent nucleus loses four nucleons.
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When a nucleus emits a beta particle, the nucleon number:
Reasoning: Beta decay converts a neutron into a proton (or vice versa), so total nucleons remain constant.
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In beta minus decay, a neutron changes into:
Reasoning: A neutron converts into a proton while emitting an electron and antineutrino.
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During beta minus decay, the atomic number:
Reasoning: A neutron becomes a proton, increasing the number of protons by one.
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Which quantity remains unchanged during beta decay?
Reasoning: A neutron converts into a proton, so the total number of nucleons does not change.
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Consider the reaction: $\mathbf{\ }_{\mathbf{92}}^{\mathbf{238}}\mathbf{U\ }\overset{\mathbf{\ \ \ \ \ \ \ \ \ \ \ }}{\rightarrow}\mathbf{\ }_{\mathbf{90}}^{\mathbf{234}}\mathbf{Th + X}$. The particle $\mathbf{X}$ must be:
Reasoning: Mass number decreases by $\mathbf{4}$ and charge decreases by $\mathbf{2}$, which corresponds to alpha emission.
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Gamma emission from a nucleus causes:
Reasoning: Gamma rays are electromagnetic radiation and contain no nucleons or charge.
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Which nuclear process conserves nucleon number but changes charge?
Reasoning: Beta decay changes a neutron into a proton or vice versa while keeping total nucleons constant.
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The conservation of charge in a nuclear reaction means:
Reasoning: The total electric charge of all particles remains conserved during nuclear processes.
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In nuclear equations, the lower number written beside an element symbol represents:
Reasoning: The atomic number represents the number of protons and hence the nuclear charge.
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In a nuclear equation, if the nucleon numbers do not balance, it indicates:
Reasoning: A valid nuclear equation must satisfy conservation of nucleon number.
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Which reaction satisfies nucleon number conservation?
Reasoning: Mass numbers balance: $\mathbf{12 = 10 + 2}$Charges balance: $\mathbf{6 = 5 + 1}$
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In nuclear fission, although the original nucleus splits into smaller nuclei:
Reasoning: The nucleons are redistributed among the products but total nucleon number remains constant.
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Nuclear fusion obeys conservation laws because:
Reasoning: Fusion combines nuclei while conserving total nucleon number and charge.
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In the reaction: $\mathbf{\ }_{\mathbf{1}}^{\mathbf{2}}\mathbf{H +}\mathbf{\ }_{\mathbf{1}}^{\mathbf{3}}\mathbf{H\ \ }\overset{\ \ \ \ \ \ \ \ \ \ \ }{\rightarrow}\mathbf{\ }\mathbf{\ }_{\mathbf{2}}^{\mathbf{4}}\mathbf{He + X}\mathbf{\ }$. The particle $\mathbf{X}$ is:
Reasoning: Nucleon numbers: $\mathbf{2 + 3 = 5}$, helium has $\mathbf{4}$, leaving $\mathbf{1}$ neutron.Charge: $\mathbf{1 + 1 = 2}$, helium already has charge $\mathbf{2}$.
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Which particle has zero charge but contributes to nucleon number?
Reasoning: Neutrons have no electric charge but are counted as nucleons.
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The atomic number of an element changes during:
Reasoning: Beta decay changes a neutron into a proton or a proton into a neutron, altering atomic number.
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A nuclear reaction is possible only if:
Reasoning: Conservation of nucleon number and charge are fundamental requirements for nuclear equations.
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The total charge of reactants compared with products in a nuclear reaction is:
Reasoning: Electric charge is a conserved quantity.
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If a neutron is emitted during a nuclear reaction, the atomic number:
Reasoning: A neutron has no charge, so emitting it does not change the number of protons.
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Which statement is false about nuclear conservation laws?
Reasoning: Nuclei can change into different nuclei while still conserving nucleon number and charge.
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A proton emission from a nucleus causes:
Reasoning: A proton contributes one nucleon and one positive charge.
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The most important reason for balancing nuclear equations is to verify:
Reasoning: Balanced nuclear equations obey conservation of nucleon number and electric charge.
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