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.*

Mathematically

Current =Voltage applied /Resistance of circuit

Resistance =Voltage applied /Current in the circuit

Potential across resistance = current x Resistance

V=I/R

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..

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

I = Voltage applied /impedance in the circuit

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