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Bihar Board Class 12 (Science) Atoms and Nuclei — practice questions — page 3

Explore 78 free Atoms and Nuclei questions in Bihar Board Class 12 (Science) Physics. Open each question or exercise to read its content, reference answers and available explanation.

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Atoms and Nuclei questions and exercises with answers

Showing questions 61–78 of 78.

NEET · Physics · Fission or FusionRead the answer and worked solution →When a nucleus $\,^{A}_{Z}\mathrm{X}$ undergoes ALPHA decay, the daughter nucleus hasRead the answer and worked solution →In BETA-MINUS ($\beta^-$) decay, the parent nucleus emits an electron AND another particle. The other particle isRead the answer and worked solution →The total binding energy of $\,^{16}_{8}\mathrm{O}$ is approximately $127.6\,\text{MeV}$. Its binding energy per nucleon is closest toRead the answer and worked solution →The unified atomic mass unit (u) is defined as exactly $1/12$ of the mass of an atom of which isotope?Read the answer and worked solution →The mass defect $\Delta m$ of a nucleus $\,^{A}_{Z}\mathrm{X}$ with mass $M$ is defined asRead the answer and worked solution →The energy equivalent of one unified atomic mass unit (1 u) is closest toRead the answer and worked solution →Order the argument: why Rutherford's atom should collapseRead the answer and worked solution →Bohr's quantisation condition for the angular momentum $L$ of an electron in the $n^\text{th}$ orbit isRead the answer and worked solution →True or false: Rutherford's two difficultiesRead the answer and worked solution →Spot the one that does not belongRead the answer and worked solution →Order the atomic models in this chapterRead the answer and worked solution →Spot the one that does not belongRead the answer and worked solution →The ratio of the first excitation energy of a hydrogen atom ($E_2 - E_1$) to its ionisation energy from the ground state isRead the answer and worked solution →A radioactive sample has half-life $T_{1/2} = 5$ years. Starting with $N_0$ undecayed nuclei, the number remaining after $20$ years isRead the answer and worked solution →Complete Bohr's first postulateRead the answer and worked solution →The radius of the $n$th Bohr orbit in a hydrogen-like atom of nuclear charge $Z$ scales asRead the answer and worked solution →The de Broglie wavelength $\lambda$ of an electron in the $n$th Bohr orbit of hydrogen, in terms of the orbit radius $r_n$, isRead the answer and worked solution →

Worked practice questions

NEET · Physics · Fission or Fusion

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Items
  1. Item
    Splitting of a heavy nucleus
    Answer
    left
  2. Item
    Combining of light nuclei
    Answer
    right
  3. Item
    Powers atomic reactors today
    Answer
    left
  4. Item
    Powers the Sun
    Answer
    right
  5. Item
    U-235 + neutron → Ba + Kr
    Answer
    left
  6. Item
    Deuterium + Tritium → Helium + n
    Answer
    right
Categories
Left
Nuclear Fission
Right
Nuclear Fusion
Instructions
Sort each property: nuclear fission or nuclear fusion?

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When a nucleus $\,^{A}_{Z}\mathrm{X}$ undergoes ALPHA decay, the daughter nucleus has

  1. mass number $A - 4$, atomic number $Z - 2$
  2. mass number $A$, atomic number $Z + 1$
  3. mass number $A - 1$, atomic number $Z + 1$
  4. mass number $A + 4$, atomic number $Z + 2$
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Correct answer: A. mass number $A - 4$, atomic number $Z - 2$

1. An alpha particle is a $\,^{4}_{2}\mathrm{He}$ nucleus — two protons and two neutrons. 2. Conservation of mass number: parent $A$ → daughter $A'$ + alpha $A_\alpha$. So $A' = A - 4$. 3. Conservation of charge: parent $Z$ → daughter $Z'$ + alpha $Z_\alpha$. So $Z' = Z - 2$. 4. Generic alpha-decay equation: $\,^{A}_{Z}\mathrm{X} \to \,^{A-4}_{Z-2}\mathrm{Y} + \,^{4}_{2}\mathrm{He}$. 5. Example: $\,^{238}_{92}\mathrm{U} \to \,^{234}_{90}\mathrm{Th} + \alpha$. 6. Option B is BETA-MINUS decay ($Z$ goes up by 1, $A$ unchanged). Option C is wrong on all counts. Option D would imply absorption rather than emission. _Source: syllabus Physics Part 2, Ch 13, §13.6 (Radioactivity — alpha decay), p. 8–9._

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In BETA-MINUS ($\beta^-$) decay, the parent nucleus emits an electron AND another particle. The other particle is

  1. a proton
  2. a neutrino
  3. a photon
  4. an antineutrino
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Correct answer: D. an antineutrino

1. The full $\beta^-$ decay equation is: $\,^{A}_{Z}\mathrm{X} \to \,^{A}_{Z+1}\mathrm{Y} + e^- + \bar{\nu}_e$. 2. The third product is an ANTI-neutrino (specifically the electron antineutrino $\bar{\nu}_e$), not a neutrino. 3. Why antineutrino? Lepton-number conservation. The electron $e^-$ has lepton number $+1$ to keep total lepton number zero on the right (as on the left), an antiparticle with lepton number $-1$ is required — that is $\bar{\nu}_e$. 4. At the quark level, $\beta^-$ decay is $n \to p + e^- + \bar{\nu}_e$ — a neutron in the nucleus converts to a proton with the emission of $e^-$ and $\bar{\nu}_e$. 5. The antineutrino is what carries away the missing energy and momentum that, without it, would have made the beta spectrum a sharp line (it is actually a continuum) — historically this is HOW the neutrino was predicted by Pauli in 1930. 6. Option A is wrong — a proton stays in the nucleus. Option B (neutrino) is reserved for $\beta^+$ decay where the daughter emits a positron and a neutrino. Option D (photon) is gamma decay, a distinct process. _Source: syllabus Physics Part 2, Ch 13, §13.6 (Radioactivity — beta decay), p. 8–9._

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