📘 Chapter 7: Thermal Properties of Matter – 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 Chapter 7 Thermal Properties of Matter including Plasma State, Mercury vs Alcohol Thermometers, Water as Thermometric Liquid, Improving Sensitivity, Specific Heat Effects, Kelvin Scale, Thermal Equilibrium, Heat vs Internal Energy, and Matter in the Sun. Each question is presented with a detailed 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 7: Thermal Properties of Matter
📋 Exercise Short Qs
📝 Short Qs
📖 Comprehensive Qs
🔢 Numerical Problems
✅ MCQs
✏️ Constructed Response
Thermal Properties of Matter covers temperature, heat, thermometers, temperature scales, and kinetic molecular theory.
📖 Constructed Response Questions & Answers (PECTAA 2026)
7.1 Is kinetic molecular theory of matter applicable to the plasma state of matter? Describe briefly.
Answer:
Yes, kinetic molecular theory is applicable to plasma because plasma consists of ionized atoms of a gas containing equal amount of positive and negative charges. Its particles are in continuous motion, like the particles of a gas.
✅ Yes, plasma particles are in continuous motion like gas particles
7.2 Why is mercury usually preferred to alcohol as a thermometric liquid?
Answer:
Mercury is usually preferred because it is a good conductor and responds quickly to the change in temperature. It also has a low freezing point and high boiling point (freezes at \(-39^\circ C\), boils at \(357^\circ C\)), so it provides a fairly long range of measurement of temperature.
✅ Good conductor | Quick response | Low freezing point (-39°C) | High boiling point (357°C) | Long range
7.3 Why is water not suitable for use in thermometers? Without calculations, guess what is equivalent temperature of \(373\,K\) on Celsius and Fahrenheit scales?
Answer:
Water is not suitable because it expands unevenly, is colourless, and is a poor heat conductor.
\[ 373\,K = 100^\circ C \]
This is the boiling point of water. On the Fahrenheit scale, it is about \(212^\circ F\).
✅ Water: uneven expansion, colourless, poor conductor | 373 K = 100°C = 212°F
7.4 Mention two ways in which the design of a liquid-in-glass thermometer may be altered to increase its sensitivity.
Answer:
Two ways are:
- Use a thin-walled glass bulb to allow quick conduction of heat to the liquid.
- Use a small amount of liquid and a narrow capillary tube, so that the liquid responds more quickly to a change in temperature.
✅ Thin-walled bulb | Small amount of liquid + narrow capillary tube
7.5 One litre of water is heated by a stove and its temperature rises by \(2^\circ C\). If two litres of water is heated on the same stove for the same time, what will be the rise in temperature?
Answer:
For two litres of water heated on the same stove for the same time, the rise in temperature will be \(1^\circ C\).
✅ Rise in temperature = 1°C (twice the mass, half the temperature rise for same heat)
7.6 Why are there no negative numbers on the Kelvin scale?
Answer:
There are no negative numbers on the Kelvin scale because its zero point is absolute zero, the lowest possible temperature. Absolute zero is \(-273.15^\circ C\) and matter does not exist below absolute zero temperature.
✅ Zero point is absolute zero (-273.15°C) | Matter does not exist below this temperature
7.7 Comment on the statement: "A thermometer measures its own temperature."
Answer:
This statement is correct. A thermometer measures its own temperature when it reaches thermal equilibrium with the object whose temperature is being measured. Thus, its temperature becomes equal to the temperature of the object.
✅ Correct statement | Thermometer reaches thermal equilibrium with object
7.8 There are various objects made of cotton, wood, plastic, metals, etc. In a winter night, compare their temperatures with the air temperature by touching them with your hand.
Answer:
All these objects, if kept in the same surroundings for sufficient time, will have approximately the same temperature as the surrounding air. They may feel different to touch because different materials transfer thermal energy at different rates.
✅ All objects reach same temperature as air | Different feeling due to different rates of thermal energy transfer
7.9 Which is greater: an increase in temperature \(1^\circ C\) or one \(1^\circ F\)?
Answer:
An increase of temperature \(1^\circ C\) is greater than \(1^\circ F\) because \(1^\circ C = 1.8^\circ F\).
✅ 1°C > 1°F (since 1°C = 1.8°F)
7.10 Why would not you expect all the molecules in a gas to have the same speed?
Answer:
The molecules of a gas are randomly moving and possess different kinetic energies. Therefore, their speeds are not expected to be the same.
✅ Random motion | Different kinetic energies | Different speeds
7.11 Does it make sense to talk about the temperature of a vacuum?
Answer:
No. Temperature is related to the motion and average kinetic energy of molecules. A perfect vacuum has no molecules, so it has no molecular kinetic energy to which a temperature can be assigned.
✅ No | Vacuum has no molecules | No molecular kinetic energy
7.12 Comment on the statement: "A hot body does not contain heat."
Answer:
The statement is correct. A body does not contain heat; it contains internal energy, which is the sum of the kinetic and potential energies of its molecules. The word heat is used for energy actually in transit from a hot body to a cold body.
✅ Correct statement | Body contains internal energy, not heat | Heat is energy in transit
7.13 Discuss whether the Sun is matter.
Answer:
Yes. The Sun is made of plasma, the fourth state of matter. Plasma contains ions and electrons and has mass and volume, so the Sun is matter.
✅ Yes | Sun is made of plasma (fourth state of matter) | Has mass and volume
📐 Key Concepts – Thermal Properties of Matter (Constructed Response)
Plasma: Ionized gas (fourth state of matter) | Conducting state
Mercury: Freezes at -39°C, boils at 357°C | Good conductor, visible
Water: Not suitable for thermometers (uneven expansion, colourless, poor conductor)
Thermal Equilibrium: Thermometer reaches same temperature as object
Heat vs Internal Energy: Heat = energy in transit | Internal energy = sum of KE + PE of molecules
Absolute Zero: 0 K = -273.15°C | Lowest possible temperature
💡 Exam Tip:
For constructed response questions, write detailed answers with clear reasoning and explanations. Use definitions, formulas, and examples where required. These questions test your analytical and critical thinking skills. These questions follow the PECTAA 2026 pattern and are prepared by Subject Specialist Muhammad Tayyab.
Chapter 1Physical Quantities and Measurements
Chapter 2Kinematics
Chapter 3Dynamics
Chapter 4Turning Effect of Forces
Chapter 5Work and Energy
Chapter 6Mechanical Properties of Matter
Chapter 7✨ Thermal Properties of Matter
Chapter 8Magnetism
Chapter 9Nature of Science
📖 Complete syllabus coverage for Class 9 Physics (PECTAA 2026) – Chapters 1 to 9
Created by Hira Science Academy | Aligned with PECTAA 2026 Syllabus