Question

In the given circuit, when key $K$ is open, reading of ammeter is $I$. Now key $K$ is closed then the correct statement is:

• A. If ${\epsilon }_1>IR$, reading of the ammeter is less than $I$
• B. If $IR<{\epsilon }_1$, reading of the ammeter is greater than $I$
• C. If ${\epsilon }_1<2IR$, reading of the ammeter will be zero
• D. $\text{Reading of ammeter will not change}$

Answer 1

The correct option is B If $IR<{\epsilon }_1$, reading of the ammeter is greater than $I$


$I=\frac{{\epsilon }_2}{2R}\Rightarrow IR=\frac{{\epsilon }_2}{2}$

After closing ${\epsilon }_2-I^{\prime }R-{\epsilon }_1=0$

$\Rightarrow I^{\prime }=\frac{{\epsilon }_2-{\epsilon }_1}{R}$

${\epsilon }_1<IR\Rightarrow {\epsilon }_1<{\epsilon }_2/2\Rightarrow I^{\prime }>I$