NIOS Class 12 Physics Chapter 10 Kinetic Theory of Gases Solutions English Medium As Per New Syllabus to each chapter is provided in the list so that you can easily browse throughout different chapters NIOS Class 12 Physics Chapter 10 Kinetic Theory of Gases Notes in English and select need one. NIOS Class 12 Physics Solutions English Medium Download PDF. NIOS Study Material of Class 12 Physics Notes Paper Code: 312.
NIOS Class 12 Physics Chapter 10 Kinetic Theory of Gases
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Kinetic Theory of Gases
Chapter: 10
| Module – III: Thermal Physics |
INTEXT QUESTIONS 10.1
1. (i) A gas fills a container of any size but a liquid does not. Why?
Ans: The fundamental reason lies in the intermolecular forces and molecular behavior:
In gases, the intermolecular forces between molecules are extremely weak compared to their kinetic energy. The gas molecules move randomly with high speeds and are separated by large distances relative to their size. Since the attractive forces are negligible, gas molecules can spread out to fill any available space completely.
In liquids, intermolecular forces are significantly stronger. While liquid molecules can move and flow, they remain close together due to these attractive forces. The molecules have enough energy to move past each other but not enough to completely overcome the intermolecular attractions, so they maintain a definite volume while taking the shape of their container.
(ii) Solids have more ordered structure than gases. Why?
Ans: The structural organization depends on the balance between kinetic energy and intermolecular forces:
In solids, intermolecular forces dom8]. The molecules have very low kinetic energy and are held in fixed positions by strong intermolecular attractions. This results in a highly ordered, rigid structure where molecules can only vibrate about their fixed positions.
In gases, kinetic energy dominates over intermolecular forces. The high kinetic energy allows molecules to move freely and randomly in all directions, overcoming any weak intermolecular attractions. This results in a completely disordered structure with no fixed positions.
2. What is an ideal gas?
Ans: An ideal gas is a theoretical gas that follows the kinetic molecular theory perfectly Key characteristics include:
(a) Gas molecules behave as point masses with negligible volume compared to the container.
(b) No intermolecular forces exist between molecules except during collisions.
(c) All collisions (molecule-molecule and molecule-wall) are perfectly elastic.
(d) Molecules are in continuous random motion following Newton’s laws.
(e) The gas obeys the equation PV = nRT under all conditions.
Real gases behave like ideal gases at low pressures and high temperatures, where intermolecular forces become negligible and molecular volume becomes insignificant compared to the container volume.
3. How is pressure related to density of molecules?
Ans: From kinetic theory, the fundamental relationship is;
P = (1/3)ρc̄²
Where:
P = pressure of the gas
ρ = density of the gas (mass per unit volume)
c̄² = mean square speed of molecules
This equation shows that:
(i) Pressure is directly proportional to the density of the gas.
(ii) Pressure is directly proportional to the mean square speed of molecules.
(iii) At constant temperature, higher density leads to higher pressure.
(iv) At constant density, higher molecular speeds lead to higher pressure.
This relationship explains why compressing a gas increases its pressure, and why heating a gas increases its pressure.
4. What is meant by specific heat of a substance?
Ans: Specific heat capacity is defined as the amount of heat energy required to raise the temperature of unit mass of a substance by 1°C (or 1 K).
Mathematically: C = ΔQ/(m × Δθ)
Where:
C = specific heat capacity
ΔQ = amount of heat supplied
m = mass of the substance
Δθ = change in temperature
(i) Its SI unit: J kg⁻¹ K⁻¹
(ii) It’s an intensive property (independent of amount of substance)
(iii) Different substances have different specific heat capacities
(iv) Water has one of the highest specific heat capacities (4184 J kg⁻¹ K⁻¹)
For gases, we define two specific heat capacities: Cp and Cv because the amount of heat required differs depending on the process.
5. Define coefficient of cubical expansion.
Ans: The coefficient of cubical expansion (γ) is defined as the fractional change in volume per degree change in temperature.
Mathematically: γ = (ΔV)/(V₀ × Δθ)
Where:
γ = coefficient of cubical expansion
ΔV = change in volume
V₀ = original volume
Δθ = change in temperature
(i) Its SI unit: K⁻¹ or °C⁻¹
(ii) It represents the increase in volume per unit volume per degree rise in temperature
(iii) For small temperature changes: V = V₀(1 + γΔθ)
(iv) Related to linear expansion coefficient (α) by: γ = 3α
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