✏️ Chapter 10: Thermal Physics – Constructed Response Questions
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 constructed response questions from the official PECTAA 2026 curriculum: thermal expansion of bridges vs. glass jars, specific heat capacity comparison, evaporation in dry air, latent heat and phase change during ice melting, and thermal expansion of electric transmission wires. Each answer is presented in the exact exam-ready format.
📚 Related Resources – Chapter 10: Thermal Physics
Constructed response questions help build deeper conceptual understanding for board exams.
✏️ Constructed Response Questions & Answers (PECTAA 2026)
10.1 Why do bridges need expansion joints but glass jars with metal lids do not, even though both experience temperature changes? Discuss in terms of the nature of thermal expansion.
Bridges need expansion joints to allow them to expand and contract with temperature changes without cracking or deforming. Glass jars with metal lids do not require joints because the metal lid can expand slightly when heated (e.g., with warm water) to loosen it. The difference arises from different coefficients of linear expansion and the practical design of the structures.
Bridges need expansion joints to allow them to expand and contract with temperature changes without cracking or deforming. Glass jars with metal lids do not require joints because the metal lid can expand slightly when heated (e.g., with warm water) to loosen it. The difference arises from different coefficients of linear expansion and the practical design of the structures.
10.2 If two liquids are heated under same conditions, but one of them heats up faster, what does this indicate about the specific heat capacity?
The liquid that heats up faster has a lower specific heat capacity. Substances with lower specific heat require less heat energy to raise their temperature, so they heat and cool more quickly.
The liquid that heats up faster has a lower specific heat capacity. Substances with lower specific heat require less heat energy to raise their temperature, so they heat and cool more quickly.
10.3 Why does a liquid evaporate faster when the air is dry?
Evaporation is faster in dry air because dry air can absorb more water vapour. If the air is already humid, it slows down evaporation since the air is closer to saturation.
Evaporation is faster in dry air because dry air can absorb more water vapour. If the air is already humid, it slows down evaporation since the air is closer to saturation.
10.4 When a piece of ice melts, the temperature does not increase even though heat is supplied. Where does the energy go, and why is this important in phase change?
The supplied heat is used to break the strong bonds between solid particles, allowing them to move freely as a liquid. This is important because the energy goes into changing the state of the substance, not raising its temperature. The temperature remains constant until the entire ice melts.
The supplied heat is used to break the strong bonds between solid particles, allowing them to move freely as a liquid. This is important because the energy goes into changing the state of the substance, not raising its temperature. The temperature remains constant until the entire ice melts.
10.5 Why do electric transmission wires sag in summer and tighten in winter?
In summer, heat increases the kinetic energy of particles, causing the wire to expand and sag. In winter, cooling reduces particle movement, causing the wire to contract and tighten.
In summer, heat increases the kinetic energy of particles, causing the wire to expand and sag. In winter, cooling reduces particle movement, causing the wire to contract and tighten.
📐 Key Concepts – Thermal Physics (Constructed Response Context)
Specific Heat Capacity: \( Q = mc\Delta T \)
Latent Heat of Fusion: \( Q = mL_{f} \)
Linear Thermal Expansion: \( \Delta L = \alpha L_0 \Delta T \)
💡 Exam Tip:
For board exams, always explain the reason behind the phenomenon in constructed response questions — don't just state the fact. Mention relevant concepts like specific heat capacity, coefficients of expansion, latent heat, and molecular kinetic energy. These constructed response questions follow the official PECTAA 2026 pattern and are prepared by Subject Specialist Muhammad Tayyab.
Unit 10✨ Thermal 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 20Atomic 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