Introduction to Coulomb's law and electric field Intensity
Calculation of force acting on test charge Q due to charges q1, q2, q3 (these are source charges) is the common problem in electromagnetic. Source charge and the test charge maybe in motion. So we can make this problem easy by finding the force on test charge due to single source charge. Then we can use principle of superposition. This is the combining effect of all forces.
Electrostatics is the situation where source charges are stationary and the test charge maybe moving. Thus with the stationary source charge the field produced do not change with time. Electrostatic helps us in understanding more complicated electromagnetic models. Natural phenomena like lighting and the principles of some important industrial applications like oscilloscope are based on electrostatics.
The development of electrostatics begins with the experimental Coulomb's law (formulated in 1785) for the force between two point charges.