Nonlinear Resistor

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Before we proceed, We should have clear view about linearity.
What is linearity?
A graph which holds linear graphical picture i.e how current changes due to voltage, Its linearity.
Then what is linear resistor?
When output is propotional to Input, i.e linear condition. When a resistance resists current to flow in presence of a electrical potential force, we call it a kind of electric circuit. Here input is voltage and output is current.
Now, If we get linear graphical picture of V-I curve, then we say, that element is linear resistance.

Those elements whose V-I curves are not straight lines are called nonlinear elements because their resistance are nonlinear resistance e.g. incandescent lamp, varistors , thermistors and diodes etc.

Incandescent lamps :
Let me explain with an example. The cold resistance of a 100 w incandescent lamp is about 9.5 ohms. If that resistance stayed same with 120 V potential applied, according [like us on facebook]to ohm's law, the bulb would draw about 12.5 amp with 1500 watt(power dissipation). But hot resistance of tungsten becomes 144 ohms(15 times the cold resistance). The resulting current is 0.83 amps with 100 watt(power dissipation). So here we come to the conclusion that when tenperature is increased, resistance increases highly.

Varistors :
A varistors is an electronic component with an electrical resistance that varies with the applied voltage. It is a voltage dependent metal-oxide material whose resistance decreases sharply with increasing voltage. There is a corresponding rapid decrease in resistance when the current increases. So it is used to provide over voltage protection.
The zinc-oxide based varistors are primarily used for protecting solid-state power supplies from low and medium surge voltage in the line. And silicon-carbide varistors provide protection against high-voltage surge.

Thermistors:
   A thermistors is a type of resistors whose resistance is dependent on temperature, more so than in standard resistors. Thermistor is made of metallic oxides in a suitable binder and has a large negative coefficient of resistance i.e its resistance decreases with increase in tempt.

Diodes:
    In electronics, a diodes is a two-terminal electronic component that conducts primarily in one direction, It has low resistance to the current in one direction and high resistance in the other. It has also a non-linear graph. When voltage continue increases, current increases high suddenly.
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