Electric Current and Theory of Electricity

What is Electric Current?

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The electric current flows in the circuit if a potential difference exists. The potential difference is the pressure that causes the flow of charge, and the flow of charge eventually leads to the 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 a large number of free electrons that can easily move from one atom to another atom under the application of potential energy. The flow of electrons or charge is the main reason for the 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 the 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 time. In other words rate of transfer of electric charge is the electric current. If the one-coulomb charge is transferred in one second from one point to another 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 does current flow in a circuit?

How does current flow in the circuit


In metal, free electrons are abundantly available which move randomly within the 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 causes the current to flow.


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


The direction of the flow of electric current is opposite to the direction of the flow of electrons. The current which flows from the higher to the lower potential point is the conventional direction of the 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 the one-directional flow of electric charge. Thus, the DC current is unidirectional.
In a DC circuit, the electrons flow from an area of negative charge to an area of negative charge. Therefore, the DC current flow from an area of positive charge area to a negative charge area because the direction of flow of current is opposite to the direction of flow of electrons.

Alternating current(AC) 

alternating current



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

Heating Effect of Current

Electric current flows in a circuit on the application of a 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

Where,

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

A magnetic field is set up around the current-carrying conductor. We can find the direction of the magnetic field using the 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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