Question

A lamp in which $10amp$ current can flow at $15V$ , is connected with an alternating source of potential $220V$ . The frequency of source is $50Hz$ . The impedance of choke coil required to light the bulb is:

• A. $0.07H$
• B. $0.14H$
• C. $0.28H$
• D. $1.07H$

Answer 1

Answer: (A)

The resistance of lamp
$R=\frac{V}{I}=\frac{15}{10}=1.5\Omega$
(Given : $V=15$ volt, $I=10amp$, A.C. voltage $=220V,f=50Hz$ ) The impedance of circuit
$Z=\frac{V}{I}=\frac{220}{10}=22ohm$
Again impedance $Z=\sqrt{R^2+{\omega }^2{L}^2}$
or $22=\sqrt{(1.5{)}^2+(2\times \pi \times 50{)}^2{L}^2}$
or $(22{)}^2=(1.5{)}^2+4{\pi }^2\times 50^2\times L^2$
or $L=0.07$ henry