An Overview of Ncert Books Class 11 Physics Chapter 13 Free Download
FAQs on Ncert Books Class 11 Physics Chapter 13 Free Download
1. What are the key postulates of the kinetic theory of gases that are frequently asked in the Class 11 Physics exam?
For the CBSE Class 11 exam, the most important postulates of the kinetic theory of gases to remember are:
- All gas molecules are in continuous, random motion.
- The volume of the gas molecules is negligible compared to the volume of the container.
- There are no intermolecular forces of attraction or repulsion between gas molecules.
- Collisions between molecules and with the container walls are perfectly elastic.
- The average kinetic energy of gas molecules is directly proportional to the absolute temperature of the gas.
2. Which derivations from Kinetic Theory are considered important 5-mark questions for the 2025-26 board pattern?
The most crucial derivation from this chapter, often appearing as a long-answer or 5-mark question, is the expression for the pressure exerted by an ideal gas. A thorough understanding of the steps involved in deriving P = (1/3)ρv²rms is essential for scoring full marks. You should also be prepared for questions that ask you to relate this pressure formula to the kinetic energy of the gas.
3. How does the kinetic interpretation of temperature connect the microscopic world of molecules to the macroscopic property we measure?
The kinetic interpretation of temperature provides a fundamental link between molecular motion and heat. It states that the absolute temperature (a macroscopic property measured with a thermometer) of a gas is a direct measure of the average translational kinetic energy of its molecules (a microscopic property). This means when you heat a gas, you are increasing the average speed and kinetic energy of its constituent molecules.
4. What types of numerical problems based on degrees of freedom and the law of equipartition of energy are important for the exam?
Important numericals often involve calculating the total internal energy and specific heats (Cv and Cp) for different types of gases. Expect questions where you must first identify the degrees of freedom for a given gas (monatomic, diatomic, or triatomic) and then apply the law of equipartition of energy, which assigns (1/2)kT of energy per degree of freedom, to find the molar specific heats and their ratio (γ).
5. Why is the root mean square (rms) speed a more significant measure for gas molecules than the simple average speed?
The rms speed is more significant because gas molecules move randomly in all directions. A simple average of their velocities would be close to zero, as velocities are vector quantities and would cancel each other out. The rms speed, however, involves squaring the velocities first (making them all positive), then taking the mean, and finally the square root. This provides a meaningful, non-zero measure of the typical speed of molecules, which is directly related to the gas's kinetic energy and temperature.
6. Under what conditions do the assumptions of the kinetic theory for an ideal gas fail to apply to real gases?
The ideal gas assumptions fail for real gases under conditions of high pressure and low temperature. This is because:
- At high pressure, molecules are forced closer together, and the volume of the molecules themselves is no longer negligible compared to the container volume.
- At low temperature, molecules move slower, and the weak intermolecular forces of attraction (van der Waals forces), ignored in the ideal model, become significant enough to affect their motion.
7. What is the importance of 'mean free path' in the kinetic theory of gases?
The concept of mean free path is crucial as it represents the average distance a gas molecule travels between successive collisions. It helps explain transport phenomena in gases, such as diffusion, viscosity, and thermal conductivity. While the kinetic theory assumes molecules are point masses that travel in straight lines, the mean free path provides a more realistic understanding of the actual, interrupted journey of a molecule within the gas, which is essential for more advanced applications of the theory.











