Ohm’s Law

The electric current I flowing through a substance is proportional to the voltage V across its ends, i.e.,

V ∝ I

V = RI,

where R is called the resistance of the substance.

The unit of resistance is ohm: 1Ω = 1 V A-1.

The resistance R not only depends on the material of the conductor but also on the dimensions of the conductor.

Important Points related to Ohm’s Law:

Ohm’s Law,


Unit: Current I in ampere (A) , potential difference V is in volt (V)

Resistance of a uniform conductor,

Resistance of a uniform conductor,

Unit: ohm (Ω)

Resistivity or specific resistance,

Resistivity or specific resistance

Unit: Ωm



Unit: ohm-1 or mho or Siemens(S)

Conductivity = 1/Resistivity

Unit: Ω-1m-1

Current density = Current/Area

Unit: Am-2


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