The idea of electric charge is the basic principle for explaining all electrical phenomena.
We identify from basic physics that each one matter is formed of basic building blocks referred to as atoms which each atom contains an electrons, protons, and neutrons. we have a tendency to conjointly apprehend that charge e on electron is negative and the same in magnitude to 1.602×10-19 c, whereas a proton transmits a positive charge of an equivalent magnitude because the electron. The existence of equivalent numbers of electrons and protons leaves an atom neutrally charged.
The following points should be noted about electric charge:
1. The coulomb is a great unit for charge. One coulomb of charge = 6.24 × 1018 electrons.
2. The charge law of conservation states that the charge can simply transfer cannot be created nor destroyed. Hence the arithmetical addition of the electric charges in a system does not change.
We currently contemplate the ﬂow of electrical charges. A singular feature of electrical charge or electricity is that the undeniable fact that it's mobile; that's, it will be moved from one place to a different, wherever it will be transformed to a different variety of energy.
When a wire (containing of many atoms) is joined to electric battery (a source of EMF), the charges are constrained to transfer; positive charge moves in one direction whereas negative charge moves in the other way. This wave of charges produces current. It’s standard to require this ﬂow of current because the movement of positive charges is opposite to the movement of negative charges.
The relationship amongst the charge q, current i and time t is
i=dq/dt ----> 1
The charge transmitted between time t0 and t is achieved by integrating the Eq: 1 on both sides. We obtain
q= to∫t idt ----> 2
In case the current not changing periodically with respect to time, but ruins constant, then said to be a direct current (dc).
By treaty the symbol I is denoted such a perpetual current. A time varying current is denoted by the symbol i. A general form of time varying current is the alternating current (ac) or sinusoidal current.
This type of current is used in your domestic, to run the washing machine, refrigerator, ac and other electrical appliances. Figure above shows alternating current and direct current; these are the two common kinds of current.
As soon as we deﬁne current as the drive of charge, we expect current to have related direction of movement. As stated previously, the direction of flow of current is conservatively taken as the direction of movement of positive charge. Based on this convention, a current of 5 amps may be signified positively or negatively shown in Fig. below. In other words, a negative current of −5 amps ﬂowing in one direction also shown below is the similar as a current of +5 amps ﬂowing in the reverse direction.