# Define the electric current class 12th

## Define the electric current

The branch of physics which deals with the charge in motion is called current electricity.
The flow of charge in definite direction is called electric current.
The rate of flow of charge through the cross-section of conductor is called electric current

In details
We know that the electric potential of a body is defined as the the degree of electrification and it determines the direction of flow of charge.
Consider two bodies A and B charged to potential V1 and V2,respectivly such that V1 is greater than V2. If they not connected with each other then their is no flow of charges hence the potential differ is remains same as it is.
If they are connected with a good conductor, the positive charge flow from higher potential body to lower potential body or the negative charge means electrons move from lower potential region on higher potential till the potential become equal in both body.
This is an instantaneous process. With in a fraction of second the charge adjust themselves. There is no movement of charge after the equalisation of electric potential.
Now connect A and B to the terminal of source S having emf. Source S help for maintaining the potential difference between two bodies. As a result the charge keep moving through the conductor.

Symbol for electric current - i
If q is the amount of charge flow through the conductor in t second,
Then, formula for electric current :-
i = q/t
Electric current flowing through a conductor is associated with magnitude as well as direction . But here, the electric current is a scalar quantity.
Whenever we want to calculate resultant current through the wire we have to take algebraic  sum of all current. It is Olly valid for scalar quantity,we take current to be scalar.
Electric current SI unit :-
Coulomb /sec
Or ampere

Instantaneous current = dq/dt
If q=1C and t= 1s
Then, i =1A
Define one ampere
The current flowing through a conductor is said to be one ampere if a charge of one Coulomb flow across any of its cross-section in one second.
The direction of current is always opposite to the  direction of flow of electrons.

### Electric current types

1. Steady current
A current is said to be steady current if its magnitude is constant and direction is always same.
2. Varying current
When the magnitude of the current change but the direction is not change periodically then the current is called varying current.
3. Alternating current
The current in which the magnitude is varies with directions continuously is called alternating current.

#### Conventional current

By convention the direction of flow of electric current is taken to be the direction of flow of positive charge.
The current in that sense called conventional.
The direction of conventional current is from A to B if the positive charge move grim A to B. A negative charge A to B is equivalent to a current flowing from B to A.

Important notes on define the electric current
1. A current taken to be along the direction of motion of electrons is called electronic current.
2. A current taken to be opposite to the motion of electron is conventional current. In physics, we often deals with conventional current.

### Description of current flow in a conductor

A metallic conductor contain large number of free electrons which act as charge carrier.
These electrons are continuously in random motion through the conductor. They collide with each other and also heavy positively charged metallic ion and change its direction in each collision.
The velocity of electron inside the conductor is very high.
When we apply a potential difference between the two terminal of electric conductor, an electric field is appear inside it.
The electric field push the free electrons from the region of lower potential to higher potential. Due to this each electrons gain extra speed towards positive terminal.
The gain in speed is how ever, oppose the successive collisions. As a result the electrons gets displace from lower to higher potential with only a small velocity know as drift velocity.
The velocity with which the free electrons are drifted toward the positive terminal, under the action of applied electric field, is called drift velocity.

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