CBSE Class 11 Physics Chapter-10 Important Questions - Free PDF Download
FAQs on Important Questions for CBSE Class 11 Physics Chapter 10 - Thermal Properties of Matter
1. What are the most important topics in Chapter 10, Thermal Properties of Matter, for the CBSE Class 11 exams 2025-26?
For the Class 11 Physics exam, the most frequently tested topics from this chapter that students must focus on are:
- Thermal Expansion: Understanding linear, area, and volume expansion, including the relationship between their coefficients (α, β, γ).
- Calorimetry: Problems involving specific heat capacity (s) and latent heat (L), often based on the principle of mixtures (heat lost = heat gained).
- Heat Transfer: The three modes—conduction, convection, and radiation—are critical. Pay special attention to thermal conductivity, Stefan's Law, and Newton's Law of Cooling.
- Anomalous Expansion of Water: This is a favourite topic for conceptual and reasoning-based questions.
2. What types of numerical problems are expected from Thermal Properties of Matter in the exam?
You should practice numericals from the following areas, as they carry significant weightage:
- Calorimetry: Calculating final temperature when different substances are mixed. For example, mixing ice at 0°C with water at a higher temperature. These problems use the formulas Q = msΔT and Q = mL.
- Thermal Expansion: Calculating the change in length or volume of solids (like metal rods or spheres) when the temperature changes, using ΔL = LαΔT.
- Newton's Law of Cooling: Problems involving calculating the time it takes for a body to cool from one temperature to another.
- Stefan's Law of Radiation: Questions on calculating the rate of heat loss or comparing the rates of heat loss from two different bodies.
3. How can I structure my answers for 3-mark and 5-mark questions from this chapter?
To score full marks, structure your answers as follows:
- For a 3-mark question: Typically a short numerical or a conceptual reasoning question. Start by stating the relevant formula or principle. Show the substitution of values clearly and write the final answer with the correct S.I. unit. For a 'why' question (e.g., about anomalous expansion), provide 2-3 distinct points explaining the phenomenon and its consequence.
- For a 5-mark question: This is often a detailed derivation (like for Newton's Law of Cooling) or a complex, multi-step calorimetry problem. For derivations, draw a labelled diagram if applicable, state all assumptions, and show the mathematical steps logically. For problems, list all given data first, then solve step-by-step, explaining each part of the calculation (e.g., heat absorbed by ice to melt, then heat absorbed by melted water to raise its temperature).
4. How are case-study based questions framed from topics like the greenhouse effect or thermal expansion?
For a case study, you might be given a short paragraph describing a real-world scenario. For example:
- Scenario: A passage describing how railway tracks are laid with small gaps between sections or how bridges have roller supports at one end.
- Expected Questions: You could be asked to (a) identify the phenomenon (linear thermal expansion), (b) explain why the gaps are necessary (to allow for expansion in summer and prevent buckling), and (c) solve a small numerical to calculate the required gap size for a given temperature change.
Similarly, a passage on a thermos flask could lead to questions on how conduction, convection, and radiation are minimised.
5. Why is the anomalous expansion of water considered important for exams, and how can it be tested?
This is a crucial concept because it's a real-world exception with significant biological importance. It's often tested in a 2 or 3-mark question. You need to explain that water has its maximum density at 4°C. As water in a lake cools, the denser water at 4°C sinks. Water colder than 4°C is less dense and stays at the surface, eventually freezing. This layer of ice insulates the water below, allowing aquatic life to survive in the liquid water. A question would require you to explain this exact process.
6. What is the fundamental difference between the three modes of heat transfer, and how can this be tested in a question?
The key difference lies in the mechanism and the medium required. For exams, you must clearly distinguish them:
- Conduction: Heat transfer through molecular collisions, without the bulk movement of the medium. It is the primary mode of heat transfer in solids.
- Convection: Heat transfer through the actual movement of the medium (fluid). Hotter, less dense fluid rises and cooler, denser fluid sinks, creating convection currents. This occurs only in liquids and gases.
- Radiation: Heat transfer via electromagnetic waves. It does not require a medium and is the fastest mode of transfer. This is how we receive heat from the sun.
A typical question might ask you to identify the dominant mode of heat transfer in different parts of a system, like a boiling pot of water or a thermos flask.
7. A common mistake is confusing heat and temperature. How can I explain the difference clearly in an exam?
To avoid losing marks, always define them distinctly. Temperature is a measure of the degree of hotness or coldness of a body, reflecting the average kinetic energy of its molecules. Its S.I. unit is the Kelvin (K). Heat, on the other hand, is the form of energy that is transferred from a hotter body to a colder body due to the temperature difference between them. Its S.I. unit is the Joule (J). In your answer, state that a temperature difference is the *cause*, and heat flow is the *effect*.
8. Why does a gas have two principal specific heat capacities, Cp and Cv? Which one is greater and why?
This is a high-level conceptual question. A gas has two specific heat capacities because its state depends on both pressure and volume.
- Cv (Specific heat at constant volume): When heat is supplied to a gas in a closed container (constant volume), all the energy goes into increasing its internal energy and raising its temperature.
- Cp (Specific heat at constant pressure): When heat is supplied at constant pressure, the gas expands. The supplied energy is used for two purposes: increasing the internal energy and doing work against the external pressure during expansion.
Therefore, Cp is always greater than Cv because more heat is required at constant pressure to achieve the same temperature rise, as some energy is used up in doing work.
9. How should I interpret a cooling curve graph based on Newton's Law of Cooling for solving questions?
A cooling curve plots the temperature of a body against time. For an exam, you should know:
- The curve is an exponential decay; it is steep initially when the temperature difference is high and becomes flatter as the body approaches the surrounding's temperature.
- The slope of the tangent (dT/dt) at any point on the curve represents the rate of cooling at that instant.
- According to Newton's Law of Cooling, this rate of cooling is directly proportional to the temperature difference between the body (T) and its surroundings (T₀). Thus, a steeper slope implies a larger temperature difference and faster cooling.
Questions may require you to compare cooling rates at different temperatures or calculate the time to cool between two points using the law's formula.











