Class 10 Physics New Syllabus 2026 | Chapter 10: Thermal Physics Notes
Welcome back to Study Hub PK! Punjab Board (PCTB) ne saal 2026 ke exams ke liye Class 10 Physics ka naya curriculum aur textbook muta-arif karwayi hai. Is naye syllabus ke mutabiq, pehla chapter ab Chapter 10: Thermal Physics hai.
Aapki behtreen tayari ke liye hum lekar aaye hain is chapter ke mukammal, accurate aur asan conceptual notes. Is post mein aapko important MCQs, Short Questions, Conceptual Questions aur complete solved Numerical Problems milenge jo bilkul aapke nayi textbook ke mutabiq hain.
🌟 Class 10 Physics New Syllabus 2026 🌟
Chapter 10: Thermal Physics Complete Notes
Exclusively Mapped for Punjab Board Students by Study Hub PK
Part A: Multiple Choice Questions (MCQs)
🌟 Class 10 Physics New Syllabus 2026 🌟
Chapter 10: Thermal Physics Complete Notes
Exclusively Mapped for Punjab Board Students by Study Hub PK
1. When the temperature of a solid object is increased, its length:
- (a) remains the same
- (b) increases (Correct)
- (c) decreases
- (d) varies randomly
- Reason: Heating increases the average distance between atoms, causing linear expansion.
2. The amount by which unit length of a material increases when the temperature is raised by 1 °C is called its:
- (a) Cubical expansion
- (b) Volume expansion
- (c) Linear expansion
- (d) Coefficient of linear expansion (Correct)
3. When a liquid is heated in a flask, the liquid level initially drops slightly because:
- (a) The liquid contracts first
- (b) The liquid evaporates immediately
- (c) The glass container expands first (Correct)
- (d) Air pressure pushes it down
4. Which property determines how much thermal energy must be added before its temperature changes significantly?
- (a) Density
- (b) Specific heat capacity (Correct)
- (c) Volume
- (d) Mass
5. High-temperature superconductors (HTS) generally exhibit their properties at temperatures:
- (a) Near absolute zero
- (b) Below 4.2 K
- (c) Up to 125 K (Correct)
- (d) Above room temperature
Part B: Short Answer Questions
Q1. What factors influence the thermal expansion of solids?
Answer: The thermal expansion of any solid body depends on three main factors:
- Initial Dimensions: The original length (L0) or volume (V0) of the solid object.
- Temperature Change (ΔT): The amount of heat energy supplied or removed.
- Nature of Material: Different materials expand differently depending on their internal atomic bond strengths, represented by their coefficients (α or β).
Q2. What are expansion loops in pipelines?
Answer: Expansion loops are intentional curves or bends built into long cross-country pipelines (such as gas or oil lines). These loops give the metal pipes space to safely expand in hot summer and contract in cold winter without cracking or bursting the line joints.
Q3. Why do liquids only experience volume thermal expansion?
Answer: Liquids do not have a fixed or definite shape of their own; they take the shape of whichever container they are poured into. Because they lack a fixed dimension in a single direction, linear or superficial expansion does not apply to them. They can only expand in all three dimensions at once, which is volume expansion.
Q4. Define Latent Heat of Fusion and state its formula.
Answer: The amount of heat energy required to completely convert 1 kg of a solid into a liquid state at its melting point, without any change in its temperature, is called the Latent Heat of Fusion (Hf).
- Formula: Hf = Q / m
Q5. What is Superconductivity?
Answer: Superconductivity is a unique physical state where certain materials show exactly zero electrical resistance when they are cooled below a specific threshold temperature called the Critical Temperature (Tc). In this state, electricity flows perfectly without any energy loss.
Part C: Conceptual Questions
Q1. Why do modern concrete bridges need expansion joints?
Answer: Concrete bridges are very long structures that experience significant changes in size between freezing winters and hot summers. Comb-like expansion joints leave empty gaps between the bridge sections, allowing them to expand and contract safely without bending the structural support pillars.
Q2. Why does a liquid evaporate faster on a hot or dry day?
Answer:
- On a hot day, the higher temperature gives liquid molecules more kinetic energy, allowing a greater number of them to break free from the surface as gas.
- On a dry day, the low humidity means the air contains very little moisture, creating more capacity to absorb water vapor quickly.
Q3. When a piece of ice melts, the temperature does not increase even though heat is supplied. Where does the energy go?
Answer: The continuous heat supplied does not increase the kinetic speed of the molecules, which is why the thermometer stays at 0 °C. Instead, all of this incoming energy is absorbed as "latent heat" to loosen and break down the rigid intermolecular bonds that hold the solid ice crystal lattice together.
Part D: Comprehensive Long Questions
Q1. Differentiate between Real and Apparent volume expansion of liquids. Write their mathematical relation.
Answer:
- Apparent Expansion (ΔVa): When we heat a liquid in a flask, the container expands first, causing the liquid level to drop briefly before rising. The visible rise that we observe from the outside is called the apparent expansion.
- Real Expansion (ΔVr): Real expansion is the true increase in the volume of the liquid. It takes into account both the visible rise of the liquid and the extra space created by the expanded glass container.
- Mathematical Relation: Real Expansion = Apparent Expansion + Container Expansion
- Formula: ΔVr = ΔVa + ΔVg
Q2. Explain the molecular mechanism of evaporation. Why does it cause a cooling effect?
Answer:
- Mechanism: Molecules inside a liquid move randomly and collide. Due to these collisions, some surface molecules gain much higher kinetic energy than average. They overcome the downward attractive forces of surrounding molecules and escape into the air as gas.
- Cooling Effect: Since only the fastest, highest-energy molecules manage to escape, the molecules left behind have a lower average kinetic energy. In physics, temperature is directly related to average kinetic energy. When the energy drops, the temperature of the remaining liquid drops, causing cooling.
Part E: Solved Numerical Problems (Step-by-Step)
Here are the complete textbook numericals solved with standard plain-text formatting, ready for your exams.
Problem 10.1
A metal rod of length 1 m expands by 0.02 m when heated from 20 °C to 120 °C. Calculate its coefficient of linear expansion.
- Given Data:
- Initial Length (L0) = 1 m
- Change in Length (ΔL) = 0.02 m
- Initial Temperature (T1) = 20 °C
- Final Temperature (T2) = 120 °C
- Change in Temperature (ΔT) = 120 °C - 20 °C = 100 °C (or 100 K)
- Formula:
- α = ΔL / (L0 × Î”T)
- Calculation:
- α = 0.02 / (1 × 100)
- α = 0.02 / 100
- α = 0.0002 K⁻¹
- Result: The coefficient of linear expansion is 2.0 × 10⁻⁴ K⁻¹
Problem 10.2
A container holds 1 litre of water at 20 °C. What will be its volume at 80 °C, assuming water's coefficient of volume expansion is 2.1 × 10⁻⁴ per °C?
- Given Data:
- Initial Volume (V0) = 1 Litre = 1000 cm³
- Initial Temperature (T1) = 20 °C
- Final Temperature (T2) = 80 °C
- Change in Temperature (ΔT) = 80 °C - 20 °C = 60 °C
- Coefficient of Volume Expansion (β) = 2.1 × 10⁻⁴ per °C
- Formula:
- Final Volume (V) = V0 × [1 + (β × Î”T)]
- Calculation:
- V = 1000 × [1 + (2.1 × 10⁻⁴ × 60)]
- V = 1000 × [1 + 0.0126]
- V = 1000 × 1.0126
- V = 1012.6 cm³
- Result: The volume of water at 80 °C will be 1012.6 cm³
Problem 10.3
A steel rod initially measures 2 m at 20 °C. If its coefficient of linear expansion is 1.2 × 10⁻⁵ °C⁻¹, what will be its length at 100 °C?
- Given Data:
- Initial Length (L0) = 2 m
- Initial Temperature (T1) = 20 °C
- Final Temperature (T2) = 100 °C
- Change in Temperature (ΔT) = 100 °C - 20 °C = 80 °C
- Coefficient of Linear Expansion (α) = 1.2 × 10⁻⁵ per °C
- Formula:
- Final Length (L) = L0 × [1 + (α × Î”T)]
- Calculation:
- L = 2 × [1 + (1.2 × 10⁻⁵ × 80)]
- L = 2 × [1 + 0.00096]
- L = 2 × 1.00096
- L = 2.00192 m
- Result: The final length of the steel rod at 100 °C will be 2.002 m
Problem 10.4
A steel bridge expands by 5 cm on a hot summer day. If the bridge originally spanned 100 m, what is the temperature change?
- Given Data:
- Change in Length (ΔL) = 5 cm = 0.05 m
- Initial Length (L0) = 100 m
- Coefficient of Linear Expansion for Steel (α) = 1.2 × 10⁻⁵ per °C
- Formula:
- ΔT = ΔL / (L0 × Î±)
- Calculation:
- ΔT = 0.05 / (100 × 1.2 × 10⁻⁵)
- ΔT = 0.05 / 0.0012
- ΔT = 41.67 °C
- Result: The temperature change experienced by the bridge is 41.67 °C
Problem 10.5
How much heat energy is required to raise the temperature of a 2 kg iron bar from 20 °C to 100 °C, given that the specific heat capacity of iron is 450 J kg⁻¹ K⁻¹?
- Given Data:
- Mass (m) = 2 kg
- Initial Temperature (T1) = 20 °C
- Final Temperature (T2) = 100 °C
- Change in Temperature (ΔT) = 100 °C - 20 °C = 80 °C (or 80 K)
- Specific Heat Capacity (c) = 450 J kg⁻¹ K⁻¹
- Formula:
- Heat (Q) = m × c × Î”T
- Calculation:
- Q = 2 × 450 × 80
- Q = 900 × 80
- Q = 72,000 Joules
- Result: The total heat energy required is 72 kJ (72,000 J)
Problem 10.6
How much heat is required to melt 500 g of ice at 0 °C into water at 0 °C? (Latent heat of fusion of ice = 3.36 × 10⁵ J kg⁻¹)
- Given Data:
- Mass (m) = 500 g = 0.5 kg
- Latent Heat of Fusion (Hf) = 3.36 × 10⁵ J kg⁻¹
- Formula:
- Heat (Q) = m × Hf
- Calculation:
- Q = 0.5 × 3.36 × 10⁵
- Q = 168,000 Joules
- Result: The heat required to melt the ice is 168 kJ (168,000 J)
Problem 10.7
Calculate the heat required to completely vaporize 1 kg of water at 100 °C. (Latent heat of vaporization of water = 2.26 × 10⁶ J kg⁻¹)
- Given Data:
- Mass (m) = 1 kg
- Latent Heat of Vaporization (Hv) = 2.26 × 10⁶ J kg⁻¹
- Formula:
- Heat (Q) = m × Hv
- Calculation:
- Q = 1 × 2.26 × 10⁶
- Q = 2,260,000 Joules
- Result: The heat required to vaporize the water is 2.26 MJ (2,260,000 J)
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