NEET Physics Notes Mechanics Thermodynamics Concept of Thermodynamics
Concept of Thermodynamics
Concept of Thermodynamics
Thermodynamics is that branch of science which deals with transformation of heat energy into mechanical energy or other forms of energy.
A thermodynamic system may be characterised by certain thermodynamic variables, e.g. pressure, volume, temperature, mass, density, etc.
Thermal Equilibrium
When there is no exchange of heat between two systems placed in contact, then both are called in thermal equilibrium.
Zeroth Law of Thermodynamics
According to this law, if two systems A and B , separated by an adiabatic wall, are separately and independently in thermal equilibrium with a third system C, then the systems A and B are also in a state of thermal equilibrium with each other.
Work
Consider a system whose volume can change (a gas, liquid or solid) in a cylinder with movable piston. Suppose, the cylinder has a cross-sectional area A and pressure exerted by system on the piston face is p.
The work done by the system on the surroundings for small displacement dx is dW – pAdx.
work done in a finite change of volume from
Note
- Area under p-l/curve (indicator diagram) gives the work done.
- Work done by the system depends on the initial and final states.
- If volume of the system increases, then work is done by the system and it is taken as positive work done.
- If volume of the system decreases, then work is done on the system and it is taken as negative work done.
Internal Energy
Internal energy of a system is defined as the sum of the total kinetic energy of all its constituent particles and sum of all the potential energies of interaction among these particles.
Note
- Internal energy of an ideal gas depends only on temperature and not on pressure and volume.
- For non-ideal gases, internal energy depends not only on the temperature but also on the pressure.
- Heat is the energy, which is transferred between system and surroundings due to the temperature difference.