What is the inductance required if a 40w-110v bulb is used with 200v-50hz ac?
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Answer:
What is the inductance required if a 40W-110V bulb is used with 220V-50Hz AC?
We know the current through the series inductor needs to be that required through the bulb which is 40W110V=0.364A .
The voltage across the inductor will be 90 degrees out of phase with the voltage across the bulb, with the combined voltage equalling 220V. Hence we can use Pythagoras to work out the voltage across the inductor to be 2202−1102−−−−−−−−−√=191V .
Therefore we know that the reactance of the inductor needs to be 191V0.364A=525Ω . Reactance of an inductor is 2πfL , so at 50Hz:
L=5252π50=1.67H
Alternatively we could use a capacitor instead of the inductor to drop the voltage. We know that the reactance of a capacitor is 12πfC , so in this case we have:
C=1525×2π50=6.06μF
Unfortunately the resulting power factor is very poor. We can calculate this simply from the voltage drop as we know that the actual power is just that used by the bulb as a pure resistance at 110V, whereas the supply voltage from which the same current is drawn is 220V. Hence the power factor is 110220=0.5
Explanation:
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