β’οΈ Chapter 20: Atomic & Nuclear Physics β Exercise Short Questions
Prepared by Muhammad Tayyab, Subject Specialist Physics, Govt Christian High School Daska. Based on PECTAA 2026 syllabus (National Curriculum 2023).
π What's Inside: This section covers 8 exercise short questions from Chapter 20 Atomic and Nuclear Physics including atomic nucleus characteristics, Rutherford's model, alpha vs beta radiation, Einstein's mass-energy equation, carbon dating principle, nuclear fusion with example, and Americium-241 alpha decay. Each question is presented with a precise answer as per the official PECTAA 2026 Physics curriculum. Perfect for Punjab Boards (Lahore, Gujranwala, Multan, etc.) and all BISE boards across Pakistan.
π Related Resources β Chapter 20
π Short Questions
βοΈ Constructed Response
π Long Questions
π Numerical Problems
β
MCQs
Atomic and Nuclear Physics covers atomic structure, isotopes, radioactivity, alpha/beta/gamma decay, nuclear fission, fusion, half-life, and carbon dating.
π Exercise Short Questions with Answers
20.1 Define the atomic nucleus. What are its two main characteristics?
Answer: Atomic nucleus is the central part of an atom which holds most of its mass. It is made up of protons and neutrons, which together known as nucleons.
Characteristics: (i) It holds most of the mass of the atom. (ii) It is made up of protons and neutrons.
β
Nucleus: central part, protons + neutrons (nucleons). Holds most mass.
20.2 What is the structure of an atom according to Rutherford's model?
Answer: According to Rutherford's model: (i) Atoms have a small, dense, and positively charged core called the nucleus. (ii) The nucleus contains most of the mass of atoms. (iii) Electrons orbit the nucleus at large distances, and the atom is mostly empty space. (iv) The nucleus is extremely small, about 10,000 times smaller than the entire atom.
OR Atoms have a small, dense, and positively charged nucleus. Electrons orbit the nucleus at large distances, and the atom is mostly empty space.
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Small, dense, positive nucleus; electrons orbit at large distances; atom mostly empty space.
20.3 How does alpha radiation differ from beta radiation?
Answer: Alpha particles (Ξ±) are helium nuclei, consisting of 2 protons and 2 neutrons each. Beta particles (Ξ²) are high-energy electrons (\(_{-1}^{0}e\)) or positrons (\(_{+1}^{0}e\)) emitted from the nucleus.
OR Alpha particles (Ξ±) are helium nuclei, consisting of 2 protons and 2 neutrons each. They carry a +2e charge (\(e = 1.6 \times 10^{-19} C\)), and are relatively large and heavy [4 atomic mass units, u]. Beta particles (Ξ²) are high-energy electrons or positrons emitted from the nucleus. They carry a β1e charge (electrons) or +1e charge (positrons) and have a very small mass.
β
Alpha: helium nucleus (2p+2n), +2e, heavy. Beta: electron/positron, Β±1e, light.
20.4 What is the primary energy source of the Sun and other stars?
Answer: The Sun and stars shine because of fusion reactions, where four hydrogen nuclei fuse into one helium nucleus, releasing about 25.7 MeV of energy.
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Nuclear fusion: 4 hydrogen β 1 helium + 25.7 MeV energy.
20.5 Name the equation proposed by Einstein that relates energy and mass.
Answer: Einstein's equation \(E = mc^2\) helps to calculate the energy released in nuclear reactions like fission and fusion. It states that a small amount of mass \((m)\) converts into a large amount of energy \((E)\).
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\(E = mc^2\): mass-energy equivalence.
20.6 What is the principle behind carbon dating and its applications?
Answer: This technique is based on the radioactive decay of carbon-14, a type of carbon found in the atmosphere. Carbon dating is an essential tool in archaeology, geology, and anthropology, helping researchers determine the age of artifacts, fossils, and other remains.
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Based on C-14 radioactive decay; used to date artifacts, fossils, remains.
20.7 Define nuclear fusion with an example.
Answer: Nuclear fusion is a process where two or more light nuclei (like hydrogen isotopes) combine to form a heavier nucleus, releasing a huge amount of energy. For example, when deuterium and tritium fuse, they form helium (alpha particle) and release energy. Equation: \(_{1}^{2}\mathrm{H} + _{1}^{3}\mathrm{H} \rightarrow _{2}^{4}\mathrm{He} + _{0}^{1}\mathrm{n} + \text{Energy}\).
β
Light nuclei combine β heavier nucleus + energy. Example: Deuterium + Tritium β Helium + neutron + energy.
20.8 Americium-241 (\(^{241}_{95}\mathrm{Am}\)) undergoes alpha decay and produces an alpha particle. Write down the nuclear equation for it and name the nucleus formed.
Answer: For Americium-241 (\(^{241}_{95}\mathrm{Am}\)), the decay equation is: \(^{241}_{95}\mathrm{Am} \rightarrow ^{237}_{93}\mathrm{Np} + ^{4}_{2}\mathrm{He}\). The nucleus formed is Neptunium-237 (\(^{237}_{93}\mathrm{Np}\)).
β
\(^{241}_{95}\mathrm{Am} \rightarrow ^{237}_{93}\mathrm{Np} + ^{4}_{2}\mathrm{He}\). Daughter: Neptunium-237.
π Key Formulas β Atomic & Nuclear Physics
\[ N = A - Z \]
Number of Neutrons
Number of Neutrons
\[ n = \frac{t}{T_{1/2}} \]
Number of Half-lives
Number of Half-lives
\[ N = \frac{1}{2^n} N_o \]
Remaining Quantity
Remaining Quantity
\[ E = mc^2 \]
Mass-Energy Equivalence
Mass-Energy Equivalence
Unit 10Thermal Physics
Unit 11Transfer of Thermal Energy
Unit 12Waves
Unit 13Sound
Unit 14Light
Unit 15Electrostatics
Unit 16Electricity
Unit 17Electromagnetism
Unit 18Electromagnetic Induction & EM Waves
Unit 19Electronics
Unit 20β¨ Atomic and Nuclear Physics
Unit 21Space and Environment
π Complete syllabus coverage for Class 10 Physics (PECTAA 2026) β Units 10 to 21
Created by Hira Science Academy | Aligned with PECTAA 2026 Syllabus