A variable inductor can be connected in series with a light bulb to act as a dim
ID: 2102368 • Letter: A
Question
A variable inductor can be connected in series with a light bulb to act as a dimmer. The inductance of such a variable inductor can be changed continuously over some predefined range. A. What inductance would reduce the current through a 100-W bulb to 25% of its maximum value? Assume a 120-V rms, 60 Hz source. B. Could a variable resistor be used in place of the variable inductor to reduce the current? Why is the inductor a much better choice for a dimmer? A variable inductor can be connected in series with a light bulb to act as a dimmer. The inductance of such a variable inductor can be changed continuously over some predefined range. A. What inductance would reduce the current through a 100-W bulb to 25% of its maximum value? Assume a 120-V rms, 60 Hz source. B. Could a variable resistor be used in place of the variable inductor to reduce the current? Why is the inductor a much better choice for a dimmer?Explanation / Answer
A)Xl=wl
so,
initial current=P/V
=0.8333
final current=0.25*0.833
=0.20833
so,
resistance=v^2/P
=144 ohm
0.20833=v/z
or 0.20833=120/(144^2+(2*pi*60*x)^2)^0.5
or x=1.4794 H
B)yes a variable resistance can be used to decrease the current. but that would also lead to the change in thepower consumed by the resistor. however the inductor does not consumes any real power, so it is a much better choice over resistor
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