A 60 V, 10 W lamp is to be run on 100 V, 60 Hz a.c. mains. Calculate the inductance of a chock required to be connected in series with it to work the bulb.

Explanation

Given : P=10 W , V=60 V , `V_(rms)` =100 volt
Current `I_(rms)=P//V=10//60=1//6A`
Resistance `R=V/I=60/(1//6)=60xx6=360 Omega`
Impedance `Z=V_(rms)/I_(rms)=100/(1//6)=600Omega`
`Z=sqrt(R^2+X_L^2) rArr L=sqrt(Z^2-R^2)/(2pif)=sqrt(600^2-360^2)/(2xx3.142xx60)`
L=1.273 H