# Important Heat and Thermodynamics Formulas for JEE Main and Advanced

JEE aspirants can go through some of the important Heat and Thermodynamics Formulas for a quick revision before the exams. The list contains all the formulas discussed under Heat and Thermodynamics.

## Heat and Thermodynamics Formulas

The transfer of heat from one body to the other takes place through three routes

(i) Conduction

(ii) Convection

1. Conduction

Rate of flow of heat in conduction is given by

$\frac{dQ}{dt}=-KA\frac{dT}{dx}$

K is the thermal conductivity

A is the area of cross-section

dx is the thickness

dT is the Temperature difference

2. Thermal resistance to conduction

R = L/KA

Here

k is the material’s conductivity

L is the plane thickness

A is the plane area

3. Emissivity

e = (Emissive power of a body at temperature T) / Emissive power of a black body at the same temperature

4. Kirchoff’s Law

The ratio of the emissive power to the absorptive power for the radiation of a given wavelength is the same for all substances at the same temperature and is equal to the emissive power of a perfectly black body

E(body)/a(body) = E (black body)

5. Nature of thermal radiations (Wien’s displacement law)

λmax ∝ 1/T

λmax T = b

λmax is the wavelength of the peak of the blackbody radiation curve

b = 0.282 cm-K , Wein’s constant

T is the temperature

6. Stefan- Boltzmann’s law

u = σ A T4 (for a perfect blackbody)

σ is the Stefan’s constant = 5.67 x 10-8 watt/m2K4

u /A is the energy flux

u = e σ A T4 (for a body which is not a perfect black body)

e is the emissivity (which is equal to absorptive power) which lies between 0 to 1.

7. Newton’s law of cooling

For small temperature difference between a body and its surrounding.

dθ/dt = (θ – θ0) where θ and θ0 are temperatures corresponding to the object and surroundings.

8. Temperature scales

F= 32 +(9/5)C

K = C + 273.16

F is the Fahrenheit scale

C is the Celsius scale

K is the Kelvin scale

9. Ideal Gas equation

PV= nRT

Here n is the number of moles

P is the pressure

V is the Volume

T is the Temperature

11. Van der Waals equation

(p + a(n/V)2)(V-nb) = nRT

P= Measured Pressure

a(n/V)2= correction factor to account for intermolecular forces

nb = correction factor to account for molecule size

n = number of moles

T = Temperature

V = Measured Volume

12. Thermal expansion

Linear Expansion : L = L0(1+αΔT)

Area Expansion: A = A0(1+βΔT)

Volume Expansion: V = V0(1+yΔT)

15. Relation between α,β and y for isotropic solid

α/1= β/2 = y/3

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