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Help me to calculate power absorbed and dissipated by a coil

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Newbie level 6
Sep 3, 2005
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I try to solve the below questions, but the results come out are not correct...Can u guy help me out?....

1)A coil having a reactance of 10 ohms and a resistance of 2 ohm is connected in parallel with capacitive reactance of 10 ohms. If the supply voltage is 200V calculate:
a) the reactive power absorbed by the coil
b)the reactive power gernerate by the capacitor
c) the active power dissipated by the coil
d)the apparent power of the circuit

2)A singel-phas capacitor has a rating of 30 Kvar,480V, 60Hz. Calculate its capacitance in mircrofarads.

Power questions?


This circuit is pretty easy, I dont think helping you with these questions is good for you. In item b) I dont think the word generate is correct, because a capacitor can not generate power. Question 2) also seems to be not correctly described.

Push yourself a little bit more


Re: Power questions?

This is indeed easy, however, I understand you confusion about this topic as I had it also when I was still studying.

To give you some tip, just play around the Ohm's law V= IZ, and Power Formulas.
S=VI, P=VIcosΘ and Q=VIsinΘ (be careful though when using complex form)... study these formulas and you will find out that everything you need is there already. Just dig a little deeper.

Re: Power questions?

Impedances of your circuit's branch: Inductance Zcoil=Rcoil+jXcoil, Capacitance Zc=1/(jXc).
As mentioned eralier you shoul use complex calculus and Ohm's law to find currents. For voltage you sholud make an assumption that its vector is with horizontal axis Vcomplex=Vrms [0deg which means that complex value is equal to RMS value.

Re: Power questions?

If you are not comfortable working with complex algebra to solve problems in AC circuits, and you prefer working only with absolute values, the Impedance and Power Triangle will be useful to you.

Nevertheless, use complex algebra in as much as possible, because once your used to using complex form, you will find it easy to solve problems. The triangle I mentioned above will still be useful in analyzing your solution.

Go ahead and solve it, update us the result.

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