Question

A $60W$ , $120 \, V$ bulb is connected to a $240 \, V$ , $60 \, Hz$ supply with an inductance in series. Find the value of inductance so that bulb gets correct voltage.

• A. $\frac{2.3}{\pi }H$
• B. $2\sqrt{3} \, H$
• C. $\pi H$
• D. $\frac{2 \sqrt{3}}{\pi }H$

Answer 1

Answer: (D)

$R=\frac{\left(120\right)^{2}}{60}=240 \, \Omega $ we require $i=0.5 \, A$
Or $\left|Z\right|=480 \, \Omega $
$X_{L}=\sqrt{480^{2} - 240^{2}}=240\sqrt{3} \, \Omega $
$L=\frac{ \, 240 \sqrt{3}}{60 \times 2 \pi }=\frac{2 . \sqrt{3}}{\pi }H$