ELECTRIC FORCE

There are four fundamental interactions among elementary particles, which are:

1. Strong
2. Electromagnetic
3. Gravitational
4. Weak interactions.

Each interaction is mediated by a particle.

The mediating particle in strong interaction is mesons, gravitational interaction depends on mass of the particles and electric charge is responsible in electromagnetic interaction and vector bosons are responsible in weak interactions.

• The electric charge of a particle is one of its fundamental properties. It exists in either positive or negative form.
• The algebraic sum of charges in an electrically insulated system does not change. This statement is called conservation of electric charge.
• Electric charge is relativistic invariant.

ELECTRIC FIELD

When a charge is kept at a point, it creates a field and this field eventually carries out interactions. Any electric charge when kept in the field alters the properties of the surrounding medium. It means when a 'test charge' is placed at any point in the field, it experiences a force. By 'test charge', I mean the magnitude of such charge is too small to alter the electric field created by the original charge.

According to various experiments,

F=q₀E, Where E is the intensity of electric field.

From the above, we can conclude that electric field vector is defined as the electric force experienced by a unit test charge.

THE FIELD OF A POINT CHARGE:

It follows from the coulomb's law that intensity at a distance r from a static charge q is given by

Principle of superposition

The intensity of the field of a system of fixed point charges is equal to the vector sum of the intensities of the fields created by each charge separately:

Different types of charge distribution

GEOMETRICAL DESCRIPTION OF ELECTRIC-FIELD

Electric-field can be visualized by drawing electric field lines. Tangent at every point on this line coincides with the direction of electric field. The no. of lines per unit area normal to these lines is proportional to the magnitude of E vector.

The Gauss Theorem

Gauss's theorem is applicable only when there is some symmetry in the problem.

Three types of symmetry exist:

1. 1) spherical symmetry
2. 2) cylindrical symmetry
3. 3) plane symmetry

Only in the above cases, gauss's law can be directly applied to calculate electric field.