OHM’S LAW AND RESISTANCE

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            OHM’S LAW AND RESISTANCE

Ohm’s Law :

If the physical state i.e. temperature, nature of material and dimensions of a conductor remain unchanged then the ratio of potential difference applied across its ends to current flowing through it remains constant.

                            V = I R

R = V / I = resistance of conductor

Resistance :

SI Unit : volt/ampere or ohm ()


Conductance(G) : The reciprocal of resistance is called conductance.

                             G = 1/ R

SI Unit : ohm–1 or mho or siemens

Dimensions : [M–1 L–2 T3 A2]

The substances which obey ohm’s law are called ohmic or linear conductor. The resistance of such conductors is independent of magnitude and polarity of applied potential difference. Here the graph between I and V is a straight line passing through the origin.

» The reciprocal of slope of straight line gives resistance. 

» The substances which do not obey ohm’s law are called non ohmic or non linear conductors.

» The I–V curve is not a straight line.

Example : p-n diode, transistors, thermionic valves,

rectifiers etc.

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