Question

Find the reading of the ammeter in the circuit given above :

• A. $\frac{V}{2R}$
• B. $\frac{3V}{4R}$
• C. $\frac{2V}{7R}$
• D. $\frac{11V}{R}$

Answer 1

Answer: (B)

$\frac{3V}{4R}$

As the wire section $cd$ do not have any resistance, thus net effective resistance across $cd$ is zero.

Equivalent resistance across e and f, $R_{ef}=\frac{R}{2}\parallel R$

$\therefore$ $R_{ef}=\frac{R\times \frac{R}{2}}{R+\frac{R}{2}}=\frac{R}{3}$

Net effective resistance of the circuit $R^{\prime }=\frac{R}{2}+R_{eff}+\frac{R}{2}$

$\therefore$ $R^{\prime }=\frac{R}{2}+\frac{R}{3}+\frac{R}{2}=\frac{4R}{3}$

Thus reading of ammeter $I=\frac{V}{R^{\prime }}$

$⟹$ $I=\frac{3V}{4R}$