question_answer

As the switch S is closed in the circuit shown in figure, current passed through it is           

A)            4.5 A

B)            6.0 A

C)            3.0 A

D)            Zero

Correct Answer: A

Solution :

                   Let V be the potential of the junction as shown in figure. Applying junction law, we have or \[\frac{20-V}{2}+\frac{5-V}{4}=\frac{V-0}{2}\]  or  40 ? 2V + 5 ? V = 2V or  5V = 45 Þ V = 9V \ \[{{i}_{3}}=\frac{V}{2}=4.5A\]