Thermodynamics

First Law of Thermodynamics

The first law of thermodynamics is the application of the conservation of energy principle to heat and thermodynamic processes:

The change in internal energy of a system is equal to the heat added to the system minus the work done by the system.

Mathematically, ΔU (Change in Internal Energy) = Q (Heat added to or drawn from the system) – W (Work done by the system)

Heat

Heat may be defined as energy in transit from a high temperature object to a lower temperature object.

Some Characteristics of Heat and Mathematical Equivalent

•    Heat is also defined as the transfer of kinetic energy from one medium or object to another, or from an energy source to a medium or object.

•    The heat transfer can occur in three ways: radiation, conduction, and convection.

•    The standard unit of heat in the International System of Units (SI) is the calorie (cal).

•    One calorie is defined as the amount of energy transfer required to raise the temperature of one gram of pure liquid water by one degree Celsius, provided the water temperature is higher than the freezing point and lower than the boiling point.

•    Sometimes the kilocalorie (kcal) is specified as a unit of heat; 1 kcal = 1000 cal. This is the also called diet calorie.

•    The amount of heat contained in a body depends upon the mass of the body.

•    If W is work performed and Heat produced is H, then W/H = J or W = JH, where J is a constant called mechanical equivalent of heat. The value of J is 4.186 Joule / Calorie. This means if 4.186 Joule of work is done, 1 Calorie of heat is consumed.

Sound Waves

•    Sound is a mechanical wave that results from the back and forth vibration of the particles of the medium through which the sound wave is moving.
•    If a sound wave is moving from left to right through air, then particles of air will be displaced both rightward and leftward as the energy of the sound wave passes through it.
•    The motion of the particles is parallel (and anti-parallel) to the direction of the energy transport. This is what characterizes sound waves in air as longitudinal waves.
•    The mechanical vibrations which can be said as sound are able to travel through all forms of matter i.e. solids, liquids and gases. The matter which allows the sound to travel through it is called the medium.
•    Sound cannot travel through a vacuum.