Question

An inductor-coil having some resistance is connected to an AC source. Which of the following quantities have zero average value over a cycle? [more than one option may be correct]

• A. Current
• B. Induced emf in the inductor
• C. Joule heat
• D. Magnetic energy stored in the inductor

Answer 1

Answer: (A), (B)

The correct options are
A Current
B Induced emf in the inductor

$Z=R+jL\omega ;V_{in}=V\sin \left(\omega t\right)$
$Current=\frac{V_{in}}{Z};emfacrossinductor=\frac{V_{in}}{Z}\times jL\omega$
joule heat= $\frac{{V^2}_{in}}{Z^2}\times R$
Magnetic energy stored $=\frac{1}{2}L\frac{{V^2}_{in}}{Z^2}$
Avg current$=$zero
Avg emf across inductor$=$zero
joule heat and magnetic energy stored in inductor are non zero.