Thermal Properties of Matter is an important chapter in Class 11 Physics that deals with how materials respond to changes in temperature. It explains concepts like heat, temperature, expansion, and heat transfer, which are essential for understanding real-life phenomena.
👉 Core Idea: When heat is supplied to a body, it can change its temperature, size, or state.
1. Temperature and Heat
Temperature
Definition
Temperature is the measure of the degree of hotness or coldness of a body.
It determines the direction of heat flow:
- Heat flows from higher temperature to lower temperature.
Heat
Definition
Heat is the form of energy that is transferred between bodies due to temperature difference.
Unit
Joule (J)
Difference Between Heat and Temperature
| Heat | Temperature |
|---|---|
| Form of energy | Measure of hotness |
| Depends on mass | Independent of mass |
| Unit: Joule | Unit: Kelvin |
2. Measurement of Temperature
Thermometers
Devices used to measure temperature.
Types
- Mercury thermometer
- Gas thermometer
- Digital thermometer
Temperature Scales
Celsius Scale (°C)
Freezing point = 0°C
Boiling point = 100°C
Kelvin Scale (K)
K = °C + 273
👉 Kelvin scale is used in physics because it is an absolute scale.
3. Thermal Expansion
When temperature changes, the dimensions of a body change.
(A) Linear Expansion
Definition
Increase in length due to temperature rise.
Formula
ΔL = αLΔT
Where:
- α = coefficient of linear expansion
(B) Area Expansion
ΔA = 2αAΔT
(C) Volume Expansion
ΔV = 3αVΔT
Concept Clarity
👉 WHY expansion occurs?
Because molecules vibrate more and move apart when heated.
4. Anomalous Expansion of Water
Water behaves differently between 0°C to 4°C.
- Water contracts when heated from 0°C to 4°C
- Maximum density at 4°C
👉 Important for aquatic life survival in winter.
5. Specific Heat Capacity
Definition
Amount of heat required to raise temperature of unit mass by 1°C.
Formula
Q = mcΔT
Where:
- m = mass
- c = specific heat
Concept Clarity
👉 Substances with high specific heat take longer to heat up.
6. Calorimetry
Principle
Heat lost by hot body = Heat gained by cold body
Formula
m₁c₁(T₁ − T) = m₂c₂(T − T₂)
7. Change of State
Latent Heat
Definition
Heat required to change state without change in temperature.
Types
- Latent heat of fusion
- Latent heat of vaporization
Formula
Q = mL
8. Heat Transfer
(A) Conduction
Heat transfer without movement of particles
Example: Metal rod
(B) Convection
Heat transfer by movement of fluid
Example: Boiling water
(C) Radiation
Heat transfer without medium
Example: Sun’s heat
9. Newton’s Law of Cooling
Definition
Rate of cooling is proportional to temperature difference.
Formula
Rate ∝ (T − Tₛ)
Important Numericals
Numerical 1
Find heat required to raise 2 kg water by 10°C
Q = mcΔT = 2 × 4200 × 10 = 84000 J
Numerical 2
Find final temperature using calorimetry equation
Numerical 3
Find expansion if α, L, ΔT given
Numerical 4
Find latent heat if Q and m given
Important Formula Sheet
- Q = mcΔT
- Q = mL
- ΔL = αLΔT
- K = °C + 273
Concept Clarity (Important)
👉 WHY water has high specific heat?
Because strong intermolecular forces require more energy.
👉 WHY radiation needs no medium?
Because it travels as electromagnetic waves.
👉 WHY metals conduct heat well?
Because free electrons transfer energy quickly.
Common Mistakes
- Using °C instead of Kelvin
- Confusing heat and temperature
- Ignoring units
Conclusion
Thermal Properties of Matter explains how heat affects materials. Understanding expansion, heat transfer, and calorimetry is essential for both exams and real-life applications.
👉 Focus on concept clarity + formulas + practice.