📘 Chapter 7: Thermal Properties of Matter – Short Answer 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 short answer questions from Chapter 7 Thermal Properties of Matter including Kinetic Molecular Theory, Intermolecular Forces, States of Matter, Plasma, Temperature, Heat, Internal Energy, Thermometers, Thermometric Properties, Temperature Scales, Absolute Zero, Thermocouple, Sensitivity, Range, and Linearity. 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.
📖 Short Answer Questions & Answers (PECTAA 2026)
1 What is kinetic molecular theory of matter?
Answer:
According to the kinetic molecular theory, matter is composed of very small particles called molecules, which are always in motion. Their motion may be vibrational, rotational, or linear.
✅ Matter = small particles (molecules) in constant motion
2 What is intermolecular force?
Answer:
There exists a mutual force of attraction between the molecules known as intermolecular force.
This force depends upon the distance between the molecules and decreases with increasing distance between them.
✅ Force of attraction between molecules | Decreases with distance
3 Why do solids have a definite shape and definite volume?
Answer:
In solids, the intermolecular forces are so strong that they keep the molecules bound. The molecules are held at fixed positions but still show vibrational motion about their fixed points. Therefore, solids have a definite shape and a definite volume.
✅ Strong intermolecular forces → molecules held at fixed positions → definite shape and volume
4 Why does a liquid have a definite volume but no definite shape?
Answer:
In liquids, the intermolecular force is so weak that it cannot hold the molecules at fixed positions. The molecules can slide over each other in random directions. Therefore, a liquid possesses a definite volume but has no definite shape and acquires the shape of the containing vessel.
✅ Weak intermolecular forces → molecules can slide → definite volume but no fixed shape
5 Why does a gas have neither a definite volume nor a definite shape?
Answer:
Gas molecules are relatively far away from one another. Due to this, a gas neither possesses a definite volume nor a definite shape.
✅ Molecules far apart → no definite volume or shape
6 What is plasma?
Answer:
Plasma is a gas in which most of the atoms are ionized, containing positive ions and electrons.
Due to the presence of positive ions and free electrons, plasma is the conducting state of matter.
Examples of plasma include:
- The Sun and most other stars, which are in the plasma state.
- Plasma TVs and gas discharge tubes, which produce plasma when electric current passes through them.
- The early stage of lightning formation, known as lightning streamers, occurs due to ionized air molecules creating conducting paths through the atmosphere.
✅ Ionized gas with positive ions and free electrons | Conducting state of matter
7 Why is plasma known as the fourth state of matter?
Answer:
Since the gas in plasma state has properties which are quite different from ordinary gas, therefore, plasma is known as the fourth state of matter.
✅ Properties different from ordinary gas → fourth state of matter
8 What is meant by temperature of a body?
Answer:
Temperature of a body is defined as the degree of its hotness or coldness.
✅ Degree of hotness or coldness
9 How can temperature be defined in terms of thermal energy?
Answer:
Temperature can be defined as a physical quantity which determines the direction of flow of thermal energy.
✅ Determines direction of thermal energy flow
10 Define heat as 'energy in transit'.
Answer:
Heat is the energy which is transferred from one object to another due to the difference of temperature between the two bodies.
✅ Energy transferred due to temperature difference
11 Define internal energy.
Answer:
The sum of kinetic and potential energies of the molecules of an object is called its internal energy.
✅ Sum of kinetic and potential energies of molecules
12 What is a thermometer?
Answer:
A thermometer is an instrument used for the exact measurement of the hotness or temperature of a substance.
✅ Instrument for measuring temperature
13 What are the basic thermometric properties of a suitable material?
Answer:
Some thermometric properties are:
- It is a good conductor of heat.
- It gives quick response to temperature changes.
- It has uniform thermal expansion.
- It has high boiling point.
- It has low freezing point.
- It has large expansivity (low specific heat capacity).
- It does not wet glass.
- It does not vaporize.
- It is visible.
✅ Good conductor, quick response, uniform expansion, high boiling point, low freezing point, visible, etc.
14 What is a liquid-in-glass thermometer?
Answer:
Liquids expand on heating. So, expansion in the volume of a liquid can be used for the measurement of temperature. This is known as a liquid-in-glass thermometer.
✅ Uses expansion of liquid to measure temperature
15 Why is mercury commonly used in thermometers?
Answer:
Mercury is opaque and can be easily seen due to its silvery colour. It is also suitable for thermometer use because it expands when heated.
✅ Opaque, visible, expands uniformly when heated
16 What are the fixed points used in temperature measurement?
Answer:
For the measurement of temperature, two reference temperatures called fixed points are required.
- (i) Upper fixed point: This is the steam point, slightly above the boiling point of water at standard atmospheric pressure.
- (ii) Lower fixed point: This is the melting point of pure ice, also known as the ice point.
✅ Upper fixed point: steam point | Lower fixed point: ice point
17 Name the three temperature scales.
Answer:
The three types of temperature scales are:
- (i) Celsius or centigrade scale
- (ii) Fahrenheit scale
- (iii) Kelvin scale
✅ Celsius, Fahrenheit, Kelvin
18 What are the fixed-point values on the Celsius scale, Fahrenheit scale and Kelvin scale?
Answer:
Celsius (Centigrade) scale:
- Lower fixed point: \(0^\circ C\)
- Upper fixed point: \(100^\circ C\)
- The scale is divided into 100 equal parts, each part representing \(1^\circ C\)
Fahrenheit scale:
- Lower fixed point: \(32^\circ F\)
- Upper fixed point: \(212^\circ F\)
- The scale is divided into 180 equal parts, each part representing \(1^\circ F\)
Kelvin scale (Absolute temperature scale):
- Lower fixed point: \(273\,K\)
- Upper fixed point: \(373\,K\)
- The scale is divided into 100 equal parts, with each part representing \(1\,K\), equivalent to \(1^\circ C\)
✅ Celsius: 0°C to 100°C | Fahrenheit: 32°F to 212°F | Kelvin: 273 K to 373 K
19 What is absolute zero?
Answer:
Absolute zero is the temperature at which molecular motion ceases, and the average kinetic energy of particles becomes zero. On the Kelvin scale, it is defined as \(0\,K\), which is equivalent to \(-273.15^\circ C\) (rounded to \(-273^\circ C\) for calculations). It is the lowest possible temperature in the universe.
✅ 0 K = -273.15°C | Lowest possible temperature
20 How main scales used for the measurement of temperature are related with each other?
Answer:
Relationship between Celsius and Fahrenheit scale:
\[ T_F = \frac{9}{5} T_C + 32 \]
\[ T_F = 1.8 T_C + 32 \]
Relationship between Fahrenheit and Celsius scale:
\[ T_C = \frac{5}{9} (T_F - 32) \]
Relationship between Kelvin and Celsius scales:
\[ T_K = T_C + 273 \]
✅ \(T_F = \frac{9}{5}T_C + 32\) | \(T_C = \frac{5}{9}(T_F - 32)\) | \(T_K = T_C + 273\)
21 What is a thermocouple thermometer?
Answer:
Thermocouple thermometer is based on the flow of electric current between two junctions of two wires of different materials due to difference of temperatures at the junctions.
✅ Based on thermo-electric current from temperature difference
22 What is sensitivity of a thermometer?
Answer:
Sensitivity of a thermometer refers to its ability to detect small changes in the temperature of an object.
✅ Ability to detect small temperature changes
23 What is the range of a thermometer?
Answer:
This refers to the span of temperature, from low to high, over which the thermometer can measure accurately.
✅ Span of temperature over which thermometer measures accurately
24 What is linearity of a thermometer?
Answer:
This refers to a direct proportional relationship between the temperature and scale reading across the entire range of measurement.
✅ Direct proportional relationship between temperature and scale reading
25 What is the structure of a liquid-in-glass thermometer?
Answer:
A liquid-in-glass thermometer has a narrow and uniform capillary tube having a small bulb filled with mercury or alcohol at its lower end.
✅ Narrow uniform capillary tube + small bulb with mercury/alcohol
📐 Key Concepts – Thermal Properties of Matter (Short Questions)
Kinetic Molecular Theory: Matter = molecules in constant motion
Intermolecular Force: Attraction between molecules, decreases with distance
Temperature: Degree of hotness/coldness
Heat: Energy in transit due to temperature difference
Internal Energy: Sum of kinetic and potential energies of molecules
Temperature Scales: Celsius, Fahrenheit, Kelvin
Absolute Zero: 0 K = -273.15°C
Thermometer Parameters: Sensitivity, Range, Linearity
💡 Exam Tip:
For short answer questions, write concise and accurate answers. Use definitions, formulas, and examples where required. These questions test your understanding of fundamental concepts like kinetic molecular theory, temperature, heat vs internal energy, thermometric properties, temperature scales, and thermometer parameters. 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