Question

An c.m.f. E=4cos(1000t) volt is applied to an LR-circuit of inductance 3mH and resistance 4 ohms. The amplitude of current in the circuit is

• A. $\frac{4}{\sqrt{7}}A$
• B. $1.0A$
• C. $\frac{4}{7}A$
• D. $0.8A$

Answer 1

The correct option is D $0.8A$

The amplitude of current in the circuit

$i=\frac{v}{z}=\frac{4}{\sqrt{4^2+(1000\times 3\times {10}^{-3}{)}^2}}$

$=\frac{4}{\sqrt{16+9}}$

$\Rightarrow \frac{4}{5}$

$=0.8$A.