what is Ohm’s Law

There is a lot of  materials which contain some ‘free’ electrons which can move in response to an applied electric field. We can move these charge carriers through the material by attaching a pair of metal wires and applying a voltage between them. Ohm’s law is the most important, basic law of electricity. The relationship between the three fundamental electrical quantities: voltage (V), the current (1) and resistance(R)

In a D.C. circuit was first discovered by German scientist George Simon Ohm in (1826). When a voltage is applied to a circuit containing only resistive elements, current flows according to Ohm’s Law, which is I = V/R. If a voltage V is applied across a conductor and current (I) flows through it then according to ohm law

The magnitude of the current in metals is proportional to the applied voltage as long as the temperature of the conductor is kept constant.


          Current =Voltage applied /Resistance of circuit

        Resistance =Voltage applied /Current in the circuit

       Potential across resistance = current x Resistance


Or    V=IR

Where R is constant  which is known as the resistance of the conducting material which depend upon the nature, dimension and physical state of the conductor

For a conductor that obeys  ohm’s law .the graph of current as a function of voltage ‘V’ is a straight line passing through the origin

As R is constant the slope is constant for ohmic conductors. The ohm’s law is not valid for all conducting material. Those material for which the slope of I verse V graph is not constant are called non-ohmic material..

Ohms law

The V-I graph for a filament bulb shows that graph bend over as V and I increase ,indicating that a given change of  V causes a corresponding small change in  at larger value of V thus slope decrease with the increase of voltage.

The V-I graph for thermistor bend upward shows that resistance decrease sharply as their temperature rises. The I-V graph of a diode shows that it is also non-linear  graph. The current passes when the voltage is applied in one direction but in almost zeros when it acts in the opposite directions,

Condition for Ohm’s Law

  • Ohms law can be applied to the entire circuit or a part of a circuit
  • When ohm law is applied to the part of circuit then part resistance and the potential across the parts resistance should be used .
  • The ohm’s law can be applied to dc as well as Ac circuit however in case of Ac Circuit impedance Z is used in place of resistance .Thus
Ohms law

   I  = Voltage applied /impedance in the circuit

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