ELECTRIC CURRENT

Electric Current-

The directed flow of free electrons (or charge) is called electric current.

OR

Flow of electron is known as electric current.

OR

Rate of flow of electron in per second.

The flow of electric current can be beautifully explained by referring to Fig. a. The copper strip has a large number of free electrons. When electric pressure or voltage is applied, then free electrons, being negatively charged, will start moving towards the positive terminal around the circuit as shown in Fig. a. 

The actual direction of current (i.e. flow of electrons) is from negative terminal to the positive terminal through that part of the circuit external to the cell. However, prior to Electron theory, it was assumed that current flowed from positive terminal to the negative terminal of the cell via the circuit. This convention is so firmly established that it is still in use. This assumed direction of current is now called conventional current.

Fig. a

Unit of Current- 

The strength of electric current I is the rate of flow of electrons i.e. charge flowing per second.

 Current, I = Q/ t 

Where The charge Q is measured in coulombs and time t in seconds. 

Therefore, the unit of electric current will be coulombs/sec or ampere (A)

If Q = 1 coulomb, t = 1 sec, then I = 1/1 = 1 ampere. 

One ampere of current is said to flow through a wire if at any cross-section one coulomb of charge flows in one second. 

 Thus, if 5 amperes current is flowing through a wire, it means that 5 coulombs per second flow past any cross-section of the wire. 

Note. 1 C = charge on 625 × 10^16 electrons. 

Thus when we say that current through a wire is 1 A, it means that 625 × 10^16 electrons per second flow past any cross-section of the wire. 

I = Q/ t = ne/t 

 where e = – 1.6 × 10^–19 C ; n = number of electron.