Question

In the circuit shown in the figure, ammeter and voltmeter are ideal. If $E=4V$ and $R=15\Omega$ and $r=1\Omega$, then the reading of the ammeter is

• A. $\frac{1}{3}A$
• B. $\frac{2}{3}A$
• C. $1A$
• D. $\frac{1}{4}A$

Answer 1

The correct option is B $\frac{2}{3}A$

Equivalently the three resistors $R$ are connected in parallel and voltmeter is connected in parallel to them, and the combination is connected to the battery.

Let the current through each resistor $R$ be $i$.

From Kirchoff's voltage law,

$E-\left(3i\right)r-iR=0$

$⟹i=\frac{E}{3r+R}$$=\frac{4V}{18\Omega }$

$⟹i=\frac{2}{9}A$

Hence, reading in ammeter will be, $3i=\frac{2}{3}A$