Electric Current and Theory of Electricity

What is Electric Current?

The electric current flows in the circuit if potential difference exist. The potential difference is the pressure that cause flow of charge, and the flow of charge eventually lead to flow of electric current in the circuit. The  rate of flow of  charge is electric current.

The electric current flows from the higher potential to the lower potential. If the two points in the circuit is at the same potential, the flow of electric charge is zero hence the current is zero.The magnitude of the current depends on the rate of flow of charge from one point to another point in a given circuit.


Unit of Current

The conducting material has large number of free electrons that can easily move from one atom to another atom under application of potential energy. The flow of electrons or charge is the main reason of flow of electric current in the circuit.

The higher the rate of flow of charge, the higher the current. Let q charge flow in t time,

The current formula is;

I= q/t

If 500 Coulomb charge passes through a conductor by 100 seconds, then current is;

I = 500/100 = 5 Ampere

In differential form,

I= dq/dt

Electric current is the ratio of charge transferred in a given period of the time. In other words rate of transfer of electric charge is the electric current. If one coulomb  charge is transferred in one second from one point to another in the circuit is called the one unit current. The unit of electric current is coulomb per second.This is also known as ampere after the name of physicist Andrew Marie Ampere. The SI unit of  electric current is Ampere.

How current flows in a circuit?

How does current flow in the circuit

In metal, free electrons are abundantly available which moves randomly within metal. When we connect metal to a supply source, the source electron repels the electrons of the metal towards the higher potential of the supply source, and thus the positive point of the supply source which is at the higher potential attracts the drifted electrons. This way, the flow of electrons cause  current  flow.

Previously, it was an assumption that the flow of the electric current  happens because of positive charge. Now it has proved that drifting of electrons from the lower to higher potential point is the main reason of current flow. The flow of current caused by external field is the drift current.

The direction of the flow of electric current is opposite of the direction of flow of electrons.The current which flow from the higher to lower potential point is the  conventional direction of current.

Types of current

There are two types of electric current.

  • Direct Current (DC)
  • Alternating Current(AC)

Direct current (DC) 

direct current circuit

Direct current (DC) is one directional flow of electric charge. Thus, DC current is unidirectional.
In DC circuit, the electrons flow from area of negative charge to an area of negative charge.Therefore, the DC current flow from an area of positive charge area to an negative charge area because the direction of flow of current is opposite to direction of flow of electrons.

Alternating current(AC) 

alternating current

When the current flows in positive and negative direction alternatively in a cycle is called alternating or AC current.

Heating Effect of Current

Electric current flows in a circuit on application of voltage across the circuit. The magnitude of the current depends on the voltage V and circuit resistance R.  The rate of heat produced in the circuit depends on the resistance and the square of the current. 

H = I2 Rt


I = Current in ampere

R = Resistance in Ohms
t   = Time in Seconds
This is known as Joule’s Law of heating.

Magnetic Effect of Current

Magnetic field is set up around the current carrying conductor. We can find the direction of magnetic field using right hand rule.

magnetic effect of current

If a current carrying conductor is placed in a magnetic field the conductor experience a force.The magnitude of the force depends on the magnitude of the current through the conductor and on the  strength of  the magnetic field.The Direction of the force can be found by Fleming’s Left Hand Rule.

r force experience by current carrying conductor

The magnitude of the force can be expressed as;

F= BILSinθ

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