Thermal Properties of Matter
Thermal expansion, specific and latent heat, conduction, convection and radiation with Newton's law of cooling. (Physics › Properties of Bulk Matter, NEET UG syllabus.)
What is Thermal Properties of Matter?
The amount of heat energy required to raise the temperature of a unit mass of a substance by one ° Celsius or one Kelvin.
Key formula / rule: Linear Thermal Expansion
Key points
- Define and apply coefficients of linear, area, and volume expansion.
- Calculate heat absorbed or released during temperature changes and phase changes.
- Distinguish between conduction, convection, and radiation as modes of heat transfer.
- Apply Fourier's Law of heat conduction, Stefan-Boltzmann Law, and Wien's Displacement Law.
Common exam trap
Confusing specific heat with latent heat; specific heat involves temperature change, latent heat involves phase change.
Definitions
- Term
Specific Heat Capacity (c)
- Meaning
The amount of heat energy required to raise the temperature of a unit mass of a substance by one ° Celsius or one Kelvin.
- Term
Latent Heat (L)
- Meaning
The amount of heat energy absorbed or released by a substance during a phase change (e.g., melting, boiling) at a constant temperature.
- Term
Thermal Conductivity (k)
- Meaning
A measure of a material's ability to conduct heat. Higher k means better conductor.
- Term
Emissivity (e)
- Meaning
The ratio of the thermal energy radiated by a surface to the thermal energy radiated by a perfect black body at the same temperature and with the same surface area.
- Term
Black Body
- Meaning
An idealized physical body that absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence, and emits thermal radiation perfectly.
- Term
Anomalous Expansion of Water
- Meaning
The unusual property of water where it contracts upon heating from 0°C to 4°C, reaching its maximum density at 4°C, and then expands upon further heating.
Learning objectives
Define and apply coefficients of linear, area, and volume expansion.
Calculate heat absorbed or released during temperature changes and phase changes.
Distinguish between conduction, convection, and radiation as modes of heat transfer.
Apply Fourier's Law of heat conduction, Stefan-Boltzmann Law, and Wien's Displacement Law.
Understand and apply Newton's Law of Cooling to solve problems.
Formulae
- Name
Linear Thermal Expansion
- Note
L₀ is initial length, L is final length, α is coefficient of linear expansion, ΔT is temperature change.
- Expression
L = L₀(1 + αΔT)
- Name
Area Thermal Expansion
- Note
A₀ is initial area, A is final area, β is coefficient of area expansion. For isotropic solids, β ≈ 2α.
- Expression
A = A₀(1 + βΔT)
- Name
Volume Thermal Expansion
- Note
V₀ is initial volume, V is final volume, γ is coefficient of volume expansion. For isotropic solids, γ ≈ 3α.
- Expression
V = V₀(1 + γΔT)
- Name
Heat absorbed/released (temperature change)
- Note
Q is heat, m is mass, c is specific heat capacity, ΔT is temperature change.
- Expression
Q = mcΔT
- Name
Heat absorbed/released (phase change)
- Note
Q is heat, m is mass, L is latent heat (fusion or vaporization).
- Expression
Q = mL
- Name
Rate of Heat Conduction (Fourier's Law)
- Note
dQ/dt is heat flow rate, k is thermal conductivity, A is cross-sectional area, dT/dx is temperature gradient. For uniform rod: Q/t = kA(T₁-T₂)/L.
- Expression
dQ/dt = -kA(dT/dx)
- Name
Stefan-Boltzmann Law (radiated power)
- Note
P is power radiated, e is emissivity (0 to 1), σ is Stefan-Boltzmann constant, A is surface area, T is absolute temperature (in Kelvin).
- Expression
P = eσAT⁴
- Name
Net Power Radiated
- Note
T is body temperature, T₀ is surrounding temperature (both in Kelvin).
- Expression
Pnet = eσA(T⁴ - T₀⁴)
- Name
Wien's Displacement Law
- Note
λm is wavelength of peak emission, T is absolute temperature (in Kelvin), b is Wien's constant.
- Expression
λm T = b
- Name
Newton's Law of Cooling
- Note
dQ/dt is rate of heat loss, k is a constant, T is body temperature, T₀ is surrounding temperature. Also expressed as (T₂-T₁)/t = K((T₁+T₂)/2 - T₀).
- Expression
dQ/dt = -k(T - T₀)
Prerequisites
Basic understanding of temperature and heat.
Knowledge of states of matter (solid, liquid, gas) and phase changes.
Basic algebra and proportionality concepts.
Common mistakes
Confusing specific heat with latent heat; specific heat involves temperature change, latent heat involves phase change.
Incorrectly applying units for temperature (Celsius vs. Kelvin) in formulas like Stefan-Boltzmann Law (always use Kelvin).
Forgetting the emissivity (e) factor in radiation formulas for non-black bodies.
Not understanding the conditions for Newton's Law of Cooling (small temperature difference).
Mixing up the coefficients of linear, area, and volume expansion.
Keywords
Thermal Expansion
Specific Heat
Latent Heat
Conduction
Convection
Radiation
Stefan-Boltzmann Law
Wien's Displacement Law
Newton's Law of Cooling
Thermal Conductivity
Emissivity
Anomalous Expansion
Practice preview
What is the correct relationship between the coefficient of linear expansion (alpha), coefficient of area expansion (beta), and coefficient of volume expansion (gamma) for an isotropic solid?…
easy
100 g of water at 80 degree C is mixed with 50 g of water at 20 degree C. Assuming no heat loss to the surroundings, what is the final temperature of the mixture? (Specific heat capacity of water = 4.2 J g^-1 K^-1)…
medium
Two rods of the same length and area of cross-section are joined in series. Their thermal conductivities are K1 and K2. The equivalent thermal conductivity of the combination is:…
hard