Current Electricity:

An electric current in a metallic wire is caused by the motion of electric charges Through   the wire. The electric current is defined as the rate of flow of electric Charges across any section of the wire. In order to set up an electric current in a wire i.e. to force the charges to move through the wire, a potential difference must be applied between the two ends of the wire. Electric current is denoted by I and it is measured in amperes (A).It means the unit of current in SI system is Ampere (A).  

To get to know more about current electricity and the relation between potential Difference and current we have to study Ohm’s law.

Ohm’s law:

When a steady potential difference is applied between the two ends of a conductor. George Ohm, a German physicist, performed a number of experiments and found the relation between the potential difference and current. This relation is known as Ohm’ law which can be stated as,

If the physical state (i.e. material, dimensions and temperature) of a conductor remains the same, the electric current  flowing through the conductor is directly proportional to the potential difference across it.

If the V is the potential difference applied across the conductor and I is the current passing through the conductor, then by ohm’s law,

  I :: V  or  V :: I

 Therefore,   = Constant

This constant is called the resistance of the conductor and it is denoted by letter R.

Therefore = R

 Or  V=IR

Or I = V / R

 The SI unit of resistance is called the ohm (Ω).

The SI unit of potential difference is volt (V).

The SI unit of current is Ampere (A).

Therefore,   R (in ohms)=

It follows that R=1 ohm, if  V = 1volt and I = 1Ampere

Therefore,  1 ohm=

 Thus the resistance of a conductor is 1ohm,if the potential difference of a 1 volt applied across the conductor causes a current  of 1 ampere to flow through it.

The reciprocal of resistance is called the conductance (symbol G).

 Therefore,G = 1/R

The unit of conductance is 1/ohm , this unit is called the mho.