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HSSLIVE Plus One Physics Chapter 11: Thermal Properties of Matter Notes

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Thermal Properties of Matter explores how materials behave under changing temperature conditions. Students investigate temperature scales, thermal expansion, and heat transfer mechanisms including conduction, convection, and radiation. This chapter connects macroscopic properties like specific heat capacity and latent heat to the kinetic theory of matter, helping students understand everyday thermal phenomena from cooking to climate control systems.

Plus One Physics Notes – Chapter 11: Thermal Properties of Matter

SCERT Kerala Board

Temperature and Heat

Temperature:

  • A measure of the degree of hotness or coldness of a body
  • Determines the direction of heat flow between bodies

Heat:

  • Form of energy that flows from a higher temperature body to a lower temperature body
  • SI unit: Joule (J)

Temperature Scales:

  • Celsius scale: 0°C (freezing point of water), 100°C (boiling point of water)
  • Fahrenheit scale: 32°F (freezing point of water), 212°F (boiling point of water)
  • Kelvin scale: 273.15 K (freezing point of water), 373.15 K (boiling point of water)

Conversion formulas:

  • K = °C + 273.15
  • °F = (9/5)°C + 32
  • °C = (5/9)(°F – 32)

Thermal Expansion

Linear Expansion:

  • Increase in length with temperature
  • ΔL = αL₀ΔT
  • α = coefficient of linear expansion
  • L₀ = original length
  • ΔT = change in temperature

Area Expansion:

  • Increase in area with temperature
  • ΔA = βA₀ΔT
  • β = coefficient of area expansion
  • β = 2α (approximately)

Volume Expansion:

  • Increase in volume with temperature
  • ΔV = γV₀ΔT
  • γ = coefficient of volume expansion
  • γ = 3α (for solids)

Anomalous Expansion of Water:

  • Water contracts when heated from 0°C to 4°C
  • Beyond 4°C, water expands with increase in temperature
  • Maximum density of water occurs at 4°C

Specific Heat Capacity

Definition: The amount of heat required to raise the temperature of 1 kg of a substance by 1 K (or 1°C).

Formula: Q = mcΔT

  • Q = heat energy (J)
  • m = mass (kg)
  • c = specific heat capacity (J/kg·K)
  • ΔT = change in temperature (K or °C)

Molar Specific Heat Capacity:

  • The heat required to raise the temperature of 1 mole of a substance by 1 K
  • C = c × molar mass

Water’s high specific heat capacity:

  • c = 4186 J/kg·K
  • Helps in stabilizing Earth’s climate
  • Makes water good for cooling and heating systems

Calorimetry

Principle: Heat lost by hot body = Heat gained by cold body (in an isolated system)

Heat exchange equation: m₁c₁(T₁ – T) = m₂c₂(T – T₂)

  • m₁, m₂ = masses
  • c₁, c₂ = specific heat capacities
  • T₁, T₂ = initial temperatures
  • T = final temperature

Water equivalent:

  • Mass of water that would absorb or release the same amount of heat as the given body for the same temperature change
  • W = mc/c_water

Change of State

Latent Heat: Heat energy absorbed or released during change of state without temperature change.

Types:

  1. Latent Heat of Fusion (L_f): Heat required to convert 1 kg of solid to liquid at constant temperature
    • For water: L_f = 3.34 × 10⁵ J/kg
  2. Latent Heat of Vaporization (L_v): Heat required to convert 1 kg of liquid to vapor at constant temperature
    • For water: L_v = 22.6 × 10⁵ J/kg

Heat calculation during phase change: Q = mL

  • Q = heat energy
  • m = mass
  • L = latent heat

Heat Transfer Mechanisms

  1. Conduction:
  • Heat transfer through matter without the movement of matter
  • Rate of heat flow: Q/t = KA(T₁-T₂)/d
    • K = thermal conductivity
    • A = cross-sectional area
    • T₁-T₂ = temperature difference
    • d = thickness of material
  1. Convection:
  • Heat transfer through actual movement of matter
  • Natural convection: Due to density differences
  • Forced convection: Due to external forces (fans, pumps)
  1. Radiation:
  • Heat transfer by electromagnetic waves requiring no medium
  • Stefan-Boltzmann Law: E = σT⁴
    • E = energy radiated per unit area per unit time
    • σ = Stefan-Boltzmann constant (5.67 × 10⁻⁸ W/m²·K⁴)
    • T = absolute temperature (K)

Wien’s Displacement Law: λ_max × T = constant (2.898 × 10⁻³ m·K)

  • λ_max = wavelength of maximum intensity
  • T = absolute temperature

Newton’s Law of Cooling

Statement: The rate of cooling of a body is directly proportional to the temperature difference between the body and its surroundings.

Mathematical form: dT/dt = -k(T – T_s)

  • T = temperature of the body
  • T_s = temperature of surroundings
  • k = proportionality constant

Solution: T – T_s = (T₀ – T_s)e^(-kt)

  • T₀ = initial temperature of the body

Thermal Conductivity

Definition: The quantity of heat flowing per unit time through a unit area when the temperature gradient is unity.

Units: W/(m·K) or J/(s·m·K)

Good conductors: Metals (copper, silver, aluminum) Poor conductors (insulators): Wood, plastic, air, glass wool

Thermal Expansion Applications

  1. Bimetallic strip: Used in thermostats
  2. Expansion joints: In bridges, railway tracks
  3. **Fitting metal rims on wooden wheels
  4. Riveting: Rivets inserted hot and contract on cooling to form tight joints

Practice Problems

  1. Calculate the length of an aluminum rod at 100°C if its length at 0°C is 1 meter. (Coefficient of linear expansion of aluminum = 23 × 10⁻⁶ /°C)
  2. How much heat is required to convert 2 kg of ice at -10°C to steam at 100°C? (Specific heat capacity of ice = 2100 J/kg·K, specific heat capacity of water = 4186 J/kg·K, latent heat of fusion = 3.34 × 10⁵ J/kg, latent heat of vaporization = 22.6 × 10⁵ J/kg)
  3. A copper rod of length 1 m and cross-sectional area 4 cm² has one end at 100°C and the other at 0°C. Calculate the rate of heat transfer through the rod. (Thermal conductivity of copper = 385 W/m·K)

These notes cover the essential concepts of Thermal Properties of Matter for Plus One Physics following the SCERT Kerala Board syllabus, presented in a simplified manner for easier understanding.

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