Atoms are made up of positively charged protons and negatively charged electrons. In its equilibrium form, the negative and positive charges are equal. The electric charge is measured in coulombs and is known as the elementary charge q

q = × −1 602 10. 19 C (1.1)

where q is positive for protons and negative for electrons. The total charge of any object Q is the multiple of the elementary charge

q attained by the object. The electric charge can be static or dynamic. Static charge is acquired by the object and stayed in the object without any motion. The dynamic charge moves inside the object due to external forces.