JEE Main · 2019 · 09 Jan 2019 · Shift 1 · Current Electricity

When the switch S , in the circuit shown, is closed, then the value of current i will be

Answer: (B)

Solution

Label the junction potential

v

and apply Kirchhoff's current law there: the currents arriving from the

20

V and

10

V branches equal the current leaving through the lower branch,

\frac{20 - v}{2} + \frac{10 - v}{4} = \frac{v}{2}

. Clearing fractions gives

2 (20 - v) + (10 - v) = 2 v

, so

50 = 5 v

and

v = 10

V. The current asked for is then

i = \frac{v}{2} = 5

JEE Main · 2019 · 09 Jan 2019 · Shift 1 · Single correct option