The H-V characteristics for ohmic and non ohmic conducters

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THE H-V CHARACTERISTICS FOR OHMIC AND NON OHMIC CONDUCTORS

The conductors for which Ohm's law hold are called Ohmic conductors. Thus,these conductors obey

Τα ΔV

It means that if we plot a graph between current l' and potential difference 'AV(called IV graph), we get a straight line; as for constant resistance the slope 1/R is a straight line. However, not all the materials have straight line graph  only metals show Ohmic behavior. The graphs of filament bulb and thermistor are curved, therefore, they are termed as non-ohmic conductor

Slope =
1
V R

(A.) Metallic Conductors:

 For metallic conductors and some alloys the graph of 'I' verses 'V' is a straight line.. 
 For example,
 (A)::: when the potential difference doubled, the current through metallic conductors also doubles.

(B.) Filament Bulb:

 The graph of filament bulb that current saturates as it is increased and at large value even a large change in voltage V will show small change in current This is because the tungsten wire in the filament of the bulb heats up with the increase in applied potential difference and free electrons collide more with lattice
atoms causing the resistance to increase and
consequently the rate and the rate of change in current decreases.

(C.) Thermistor: 

Thermistor is a device whose resistance
changes significantly (highly) with temperature. Usually thermistor's resistance decreases with increase in temperature. The IV Graph of the thermistor shows that resistance decreases sharply. Thus, at a large
value even for a small change in applied voltage AV, it will show a large change in current I. 





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