Current-voltage characteristics of two elements A and B are as shown below in Figs. (a) and (b).
(a)
Which of the following graphs represents current voltage characteristics for their series combinations ?

Options

A.
B.
C.
D.

Explanation

In element `A`, the resistance remains constant upto the potential drop of `10V`. Further increase in the voltage does not increase this current (which is constant at `1A`). This means that the ratio `V//R_(A)=` constant and this resistance `R_(A)` increases linearly with voltage.
In element `B`, the resistance decreases gradually upto `15V` and afterwards the resistance `R_(B)` increases linearly with voltage.
When both `A` and `B` are in series, the current in the circuit will increase non linearly upto `1A` when the total voltage drop across `A` and `B` becomes `10+15=25V`.
Further increase in this voltage does not bring about any change in the current as shown in solution `(C )`. The voltage drop across `A` will go on increasing while that across `B` remain fixed at `15V`.