In the given circuit, an ideal voltmeter connected across the $10 \Omega$ resistance reads 2 V . The internal resistance r, of each cell is:

JEE Main · 2019 · 10 Apr 2019 · Shift 1 · Current Electricity

In the given circuit, an ideal voltmeter connected across the

10Ω

resistance reads 2 V . The internal resistance r, of each cell is:

Answer: (B)

The voltmeter reads

2

V across the

10 Ω

resistor, which is in parallel with

15 Ω

; that pair has equivalent resistance

\frac{15 \times 10}{25} = 6 Ω

. The total resistance round the loop is

R_{e q} = 6 + 2 + 2 r = 8 + 2 r

, so the current is

i = \frac{3}{8 + 2 r}

. The voltage across the parallel pair is

2 = 6 i = \frac{18}{8 + 2 r}

, and solving

16 + 4 r = 18

gives

r = 0.5 Ω

JEE Main · 2019 · 10 Apr 2019 · Shift 1 · Single correct option