Question

In the given $\text{LCR}$ series circuit, the reading $\left(\text{in A}\right)$ of the hot wire ammeter (assume all meters are ideal) is

Answer 1

$V_{\text{rms}}=\frac{V_0}{\sqrt{2}}=\frac{200\sqrt{2}}{\sqrt{2}}=200\text{V}$

Voltage across $\text{L-C}$ combination, $V_1=120\text{V}$

So, voltage across resistance is

$V_R=\sqrt{V_{rms}^2-V_1^2}=\sqrt{{200}^2-{120}^2}=160\text{V}$

$\therefore I=\frac{V_R}{R}=\frac{160}{40}=4\text{A}$

Key point : The wire ammeter measures the RMS value.