Question

The incorrect option in the given circuit if the reading of ammeter is zero is

• A. The value of $\epsilon$ will be $\frac{\epsilon (R+r)}{R}$
• B. Current in R is $\frac{{\epsilon }_1}{r+R}$
• C. Value of ${\epsilon }_1$ will be $\epsilon$
• D. Potential across 2R is zero

Answer 1

The correct option is C Value of ${\epsilon }_1$ will be $\epsilon$

$\because$ Reading in Ammeter is zero, so the current (i) will only flow in the upper circuit. Where $I=\frac{{\epsilon }_1}{R+r}$
=$i_r=i_R$,
$\therefore$ (b) is correct.
Here, $v_Q-v_R={\epsilon }_1-r{i}_r={\epsilon }_1-r.\frac{{\epsilon }_1}{R+r}=\frac{{\epsilon }_{1}R}{R+r}=\epsilon$
$\because$ no current is flowing through 2R
${\epsilon }_1=\frac{\epsilon (R+r)}{R}$
$\therefore$ (a) is correct and (c) is incorrect
$\because$ no current is flowing through 2R
$\therefore$ potential difference across 2R = 0
$\therefore$ (d) is also correct.