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- Learn important concepts of the chapter

Analogy of electric current to other phenomenon

Flow of electric current occurs only in the presence of potential difference and it flows from higher potential to lower potential. This is similar to:
  • Heat Transfer: It flows from body at higher temperature to a body at lower temperature.
  • Water flow: It flows from high pressure to low pressure.
  • Free fall: A body falls from point of higher gravitational potential to a point of lower gravitational potential. 

Electric current

Rate of flow of charge through a given cross-section of a wire is called electric current. 
It is given by the formula, 

Potential difference

The electric potential difference between two points in an electric circuit is the work done in moving a unit positive charge from one point to the other.
Potential difference,


Ohm's Law

According to Ohm's Law, the current flowing in a conductor is directly proportional to the potential difference across its ends provided the physical conditions and temperature of conductor remains constant.



Resistance() of a material is a measure of the obstruction offered to the flow of current through the material. It is caused due to inter-collisions of electrons. It is a function of the material, dimensions and the temperature of the resistor. For conductors, resistance increases linearly with temperature. It unit is .

Resistivity, function of the nature of material 
Length of the resistor
Area of the resistor 

Resistors in series

For resistors in series:


Resistors in parallel

For  resistors in parallel:


Joule's Law of heating

According to Joule's Law of heating, heat generated in a conductor is given by:

Electrical power

Electrical power is given by: 
Its unit is (Watt).