## Electrostatics

In today’s world, almost every device we use requires electricity. Electricity is a topic that everyone must understand because of its widespread application. The study of electricity requires knowledge of charges.

The electrons and protons repel or attract each other because of their property called charge. The process of charging a body is known as electrification. The process of electrification can be done by friction, conduction or induction. The science of static electricity is called electrostatics.

## Electrostatic field

The electrostatic field or simply electric field is the region surrounding the charge or a system of charges in which the other charged particles will experience an electrical force. The electric field strength also called electric intensity or simply electric field at a point is the electrostatic force per unit positive charge placed at that point. It is a vector quantity having both magnitude and direction. The SI unit of electric field strength is Newton per Coulomb (N/C).

## Electric dipole

Two equal and opposite charges separated by a small distance is called an electric dipole. The electric field produced by a dipole is called a dipole field.

## Electric Field lines

Electric field lines or the electric lines of force help us visualise the electric field pattern in the region. In an electric field, the electric field line is the imaginary path along which a unit positive charge free to move travels.

## Properties of Electric Field Lines

Electric lines of force start from the positive charge and terminate at the negative charge

The electric field vector is along the tangent to the electric field lines.

The field lines are close together when the electric field is stronger and far apart when the field is weaker.

The number of field lines is proportional to the magnitude of the charge

The electric field lines will never intersect

The electric field inside the conductor is always zero, therefore the lines of force will not pass through the conductor.

The lines of force will not form closed loops

In a uniform electric field, the lines of force will be parallel and at an equal distance

When the lines of force contract longitudinally it indicates that the force between two, unlike charges is attractive.

When the lines of force exert a lateral force on each other it shows that the electrostatic force between like charges is repulsive.

## Relation between Electric field and Electric Potential

The electric potential at any point in an electric field is defined as the amount of work done in moving a unit positive charge from infinity to that point against the electric field.  If E is the electric field intensity at point P. This means E is the force per unit positive charge placed at point P. If the unit positive charge is moved from point P to Q through a distance dx. The amount of work done in moving the charge is given by the expression

dW = - Edx (Since the work is done against the field there is a negative sign)

From the definition of electric potential, it is the amount of work done in moving a unit positive charge from P to Q. If dV is the potential difference between P and Q then, we get dV= dW

I.e., E = - dV/dx

dV/dx is the rate of change of potential with distance. It is called the potential gradient.