Question

Graph showing the variation of current versus voltage for a material Ga. As is shown in the figure, identify the region of:
(i) Negative resistance
(ii) Where Ohm’s law is obeyed.

Answer 1

Hint:To find the region where Ohm’s law is obeyed, we should know the limitations of ohm’s law and the slope must be constant. To find the region where there is negative resistance, we have to observe the slopes of the graph at every region.

Complete step by step answer:
We are given a graph showing the variation of current versus voltage for a material Ga.
We have to find the negative resistance and the region where the Ohm’s law is obeyed.
According to Ohm’s law, the current passing through a conductor is directly proportional to voltage applied across it.
Thus
$
V \propto I \\
\Rightarrow \dfrac{V}{R} = I \\
\Rightarrow \dfrac{V}{I} = R \\
$
Here we can see that for Ohm’s law to be valid, the slope of the I versus V curve should be constant and positive. The BC region in the graph is a straight line and the slope of the graph at every point in the BC region is the same and positive. Hence region BC obeys ohm’s law.
The slope of I versus V curve is negative in the region DE as the curve is descending downwards. Hence the resistance is negative in the region DE.

Note:Conductors which obey Ohm’s law have a constant resistance when the voltage is varied across them or the current through them is increased. These conductors are called Ohmic conductors. When the curve is descending then the slope is negative and when the curve is ascending the slope is positive. Be careful with this.