The second thermodynamics law.

The second law of thermodynamics asserts the existence of a quantity called the entropy of a system and further states that

When two isolated systems in separate but nearby regions of space, each in thermodynamic equilibrium in itself (but not necessarily in equilibrium with each other at first) are at some time allowed to interact, breaking the isolation that separates the two systems, allowing them to exchange matter or energy, they will eventually reach a mutual thermodynamic equilibrium. The sum of the entropies of the initial, isolated systems is less than or equal to the entropy of the final combination of exchanging systems. In the process of reaching a new thermodynamic equilibrium, total entropy has increased, or at least has not decreased.

Coulomb's law .

Coulomb's law states that the magnitude of the Electrostatics force of interaction between two point charges is directly proportional to the scalar multiplication of the magnitudes of charges and inversely proportional to the square of the distances between them.

If the two charges have the same sign, the electrostatic force between them is repulsive; if they have different sign, the force between them is attractive.

The scalar and vector forms of the mathematical equation are

and

,   respectively.

Electrostatic field.

The electric field at a point E(r) is equal to the negative gradient of the electric potential Φ(r), a scalar field at the same point:

where ∇ is the gradient. This is equivalent to the force definition above, since electric potential Φ is defined by the electric potential energyU per unit (test) positive charge:

and force is the negative of potential energy gradient:

If several spatially distributed charges generate such an electric potential, e.g. in a solid, an electric field gradient may also be defined.

Intensity of electrostatic field. Intensity of field created by point charge.

All charged objects create an electric field that extends outward into the space that surrounds it. The charge alters that space, causing any other charged object that enters the space to be affected by this field. The strength of the electric field is dependent upon how charged the object creating the field is and upon the distance of separation from the charged object. In this section of Lesson 4, we will investigate electric field from a numerical viewpoint - the electric field strength.

 

The Force per Charge Ratio

Electric field strength is a vector quantity; it has both magnitude and direction. The magnitude of the electric field strength is defined in terms of how it is measured. Let's suppose that an electric charge c an be denoted by the symbolQ. This electric charge creates an electric field; since Q is the source of the electric field, we will refer to it as the source charge. The strength of the source charge's electric field could be measured by any other charge placed somewhere in its surroundings. The charge that is used to measure the electric field strength is referred to as a test charge since it is used to test the field strength. The test charge has a quantity of charge denoted by the symbol q. When placed within the electric field, the test charge will experience an electric force - either attractive or repulsive. As is usually the case, this force will be denoted by the symbol F. The magnitude of the electric field is simply defined as the force per charge on the test charge.

If the electric field strength is denoted by the symbol E, then the equation can be rewritten in symbolic form as

.