THERMAL PROPERTIES OF MATTER
Complete NCERT Study Notes & 5-Part Mega Quiz for NEET
1. Temperature and Thermal Expansion
Temperature is a relative measure of hotness or coldness. The fundamental relation between temperature scales is:
Thermal Expansion: Most substances expand on heating and contract on cooling. The fractional change in dimension is proportional to the change in temperature.
- Linear Expansion: $\Delta L = \alpha L \Delta T$
- Area Expansion: $\Delta A = \beta A \Delta T$
- Volume Expansion: $\Delta V = \gamma V \Delta T$
For isotropic solids, $\gamma = 3\alpha$ and $\beta = 2\alpha$.
Anomalous Expansion of Water: Water uniquely contracts when heated from $0^\circ\text{C}$ to $4^\circ\text{C}$. It has its maximum density at exactly $4^\circ\text{C}$.
2. Specific Heat Capacity and Calorimetry
Specific Heat Capacity ($s$): The amount of heat required to raise the temperature of unit mass of a substance by $1^\circ\text{C}$.
Molar Specific Heat ($C$): Heat required to raise the temperature of 1 mole of a substance by 1 K. $C = \frac{1}{\mu} \frac{\Delta Q}{\Delta T}$.
Principle of Calorimetry: When two bodies at different temperatures are mixed, in an isolated system, Heat Lost by the hot body = Heat Gained by the cold body.
3. Change of State and Latent Heat
During a change of state (e.g., solid to liquid), the temperature of the substance remains constant. The heat supplied is used to break intermolecular bonds.
$$Q = m L$$
- Latent heat of fusion of ice ($L_f$) $\approx 80 \text{ cal/g} \approx 3.33 \times 10^5 \text{ J/kg}$.
- Latent heat of vaporization of water ($L_v$) $\approx 540 \text{ cal/g} \approx 22.6 \times 10^5 \text{ J/kg}$.
4. Heat Transfer: Conduction & Convection
Conduction: Heat transfer in solids without actual movement of molecules. The rate of heat flow ($H = \frac{dQ}{dt}$) in steady state is:
Where $K$ is the thermal conductivity. Thermal resistance is $R_{th} = \frac{L}{KA}$.
Convection: Heat transfer by actual bulk motion of the fluid (liquids and gases). It can be Natural (driven by gravity/density differences) or Forced (using fans/pumps).
5. Radiation and Newton's Law of Cooling
Radiation: Heat transfer through electromagnetic waves, requiring no medium. The fastest mode of heat transfer.
- Stefan-Boltzmann Law: The energy emitted per second per unit area of a blackbody is proportional to the fourth power of absolute temperature: $E = \sigma T^4$.
- Wien's Displacement Law: $\lambda_m T = b$. (Hotter objects emit shorter wavelengths).
- Newton's Law of Cooling: The rate of loss of heat is directly proportional to the temperature difference between the body and its surroundings: $\frac{dT}{dt} = -k(T - T_s)$.
🚀 NEET THERMAL PROPERTIES MEGA QUIZ (100 MCQ)
Solve the 5 parts below to master Thermometry, Calorimetry, Conduction, and Radiation.
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