question_answer

The network shown in figure is part of a complete circuit. If at a certain instant the current \[(i)\] is 5A and is decreasing at a rate of \[{{10}^{3}}\text{ }A/s,\] then \[{{V}_{B}}-{{V}_{A}}\] is

A)  5V                              

B)  10V

C)  15V                            

D)  20V

Correct Answer: C

Solution :

\[e=L\,\frac{di}{dt}\,=5\times \,{{10}^{-3}}\,\times ({{10}^{3}})\,=5V\] Polarity of emf in inductor is developed in such a maner so that it helps to increase the existing current as it is decreasing. \[{{V}_{A}}-(5\times 1)\,+15\,+5={{V}_{B}}\] \[{{V}_{B}}-{{V}_{A}}\,=15V\]