Current density—

The current density at any point inside a conductor is defined as the amount of charge flowing per sec through a unit area held normal to the direction of the flow of charge at that point.

Conductance—

The conductance of a conductor is the ease with which electric charges flow through it. It is equal to the reciprocal of its resistance and is denoted by ‘G’.

Resistance—

The resistance of a conductor is the property by virtue of which it opposes the flow of charge through it.

It is equal to the ratio of the potential difference applied across the conductor to the current flowing through it.

Its unit is Ohm or Volt/Ampere.

Definition of One ohm—

If      V=1 Volt         i=1 Amp    then

R= 1 ohm

Electromagnetic Force—

The emf of a source is equal to the maximum potential difference between its terminals when it is in open circuit that is when it is not sending any current in the circuit.

The emf of a source is defined as the energy supplied by the source in taking a unit positive charge once round the complete circuit.   

Kirchhoff’s Laws—

Kirchhoff gave two laws

1. Kirchhoff’s First law or Junction Law or Kirchhoff’s Current Law (KCL)
2. Kirchhoff’s Second Law or Loop Law or Kirchhoff’s Voltage Law (KVL)

Kirchhoff’s First law or Junction Law or Kirchhoff’s Current Law (KCL)

This law states that at a junction, the algebraic sum of all the currents is zero. In other words at a junction the sum of all the incoming currents is equal to the sum of all the outgoing currents.