A Light-Dimmer Circuit The intensity of a lightbulb with a resistance of 140ohm

Question

A Light-Dimmer Circuit The intensity of a lightbulb with a resistance of 140ohm is controlled by connecting it in series with an inductor whose inductance can be varied from to . This "light dimmer" circuit is connected to an ac generator with a frequency of 60.0hz and an rms voltage of 120V.

a. What is the average power dissipated in the lightbulb when ? The answer is 102W
b. The inductor is now adjusted L=Lmax so that . In this case, the average power dissipated in the lightbulb is one-fourth the value found in part A. What is the value of Lmax ? the answers 1.11 and 1.44 are incorrect. answer is in H.

Explanation / Answer

power=102/4=25.5 W let inductance=L then total impedance of the circuit=140 +j 377*L ohms j=sqrt(-1) so magnitude=sqrt(19600 +142129*L^2) ohms current magnitude=120/sqrt(19600 +142129*L^2) power factor angle=arctan(377*L/140) so 120*(120/(sqrt(19600 +142129*L^2) ))*cos(arctan(377*L/140))=25.5 solving we get L=0.6467 H

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.