. Which of the following graphs represents current-voltage characteristics for their series combination

Current-voltage characteristics of two elements A and B are as shown. [fig. (a) and (b) ]





Best Answer

Ans: C

Sol: In element A, the resistance remains constant upto the potential drop of 10 V.  Further increase in the voltage does not increase this current (which is constant at 1 A). This means that the ratio V/RA = constant and this resistance RA increases linearly with voltage.

In element B, the resistance decreases gradually upto 15 V and afterwards the resistance RB increases linearly with voltage. When both A and B are in series, the current in the circuit will increase non-linearly upto 1 A when the total voltage drop across A and B becomes 10 + 15 = 25 V.

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 remains fixed at 15 V.

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