☢️ Chapter 20: Atomic & Nuclear Physics – Constructed Response
Prepared by Muhammad Tayyab, Subject Specialist Physics, Govt Christian High School Daska. Based on PECTAA 2026 syllabus (National Curriculum 2023).
📖 What's Inside: This section covers 5 constructed response questions from Chapter 20 Atomic and Nuclear Physics including atom empty space & solid objects, estimating half-life, gamma ray danger, carbon dating future, and fission vs fusion. 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.
📚 Related Resources – Chapter 20
Atomic and Nuclear Physics covers atomic structure, isotopes, radioactivity, alpha/beta/gamma decay, nuclear fission, fusion, half-life, and carbon dating.
📝 Constructed Response Questions with Answers
20.1 If an atom is mostly empty space, why do not we fall through solid objects or pass through walls?
Answer: Atoms have a small, dense, and positively charged nucleus, while electrons exist in regions called electron clouds. The interaction between electrons and the electromagnetic forces between atoms prevents us from passing through solid objects.
✅ Electromagnetic forces between electrons and atoms prevent passing through.
20.2 Imagine a new radioactive element is discovered. How could scientists estimate its half-life without waiting thousands of years?
Answer: Scientists can measure the activity of the radioactive material and observe how quickly its atoms decay. By measuring the remaining radioactive isotope over time, they can estimate its half-life using the radioactive decay pattern.
✅ Measure activity and decay rate over time → use decay pattern to estimate half-life.
20.3 If gamma rays do not change the number of protons or neutrons in a nucleus, why are they still considered dangerous?
Answer: Gamma rays have very high penetration power and can pass through thick materials like lead or concrete. They have low ionizing power, but ionizing radiation can alter or damage atoms and molecules, including DNA.
✅ High penetration; can damage DNA and molecules despite low ionizing power.
20.4 If carbon-14 stopped forming in the atmosphere today, how would that affect the use of carbon dating in the future?
Answer: Living organisms constantly absorb carbon-14 while they are alive. If carbon-14 stopped forming, the existing carbon-14 would continue to decay at a fixed rate, so carbon dating could still be used for materials containing carbon-14, but its usefulness would eventually decrease as less carbon-14 remained.
✅ Carbon dating still possible until C-14 runs out; usefulness decreases over time.
20.5 What is the difference between nuclear fission and nuclear fusion in terms of process and energy release?
Answer: In fission reaction, a heavy nucleus like Uranium-235 splits into two smaller nuclei, releasing a large amount of energy and additional neutrons. In nuclear fusion, two or more light nuclei like hydrogen isotopes combine to form a heavier nucleus, releasing a huge amount of energy.
✅ Fission: splits heavy nucleus → releases energy + neutrons. Fusion: combines light nuclei → releases huge energy.
📐 Key Formulas – 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 20✨ Atomic and Nuclear Physics
Unit 21Space and Environment
📖 Complete syllabus coverage for Class 10 Physics (PECTAA 2026) – Units 10 to 21
Created by Hira Science Academy | Aligned with PECTAA 2026 Syllabus