# Power problem

Discussion in 'Homework Help' started by metelskiy, Feb 23, 2011.

1. ### metelskiy Thread Starter Member

Oct 22, 2010
66
3
I have 3 different problems:
1. A 0.5H inductor has a resistance of 150 ohms. The current flowing through the inductor is 0.4A at a frequency of 60Hz.What is the real power dissipated by the inductor?
2.A 0.5H inductor has a resistance of 150 ohms. The current flowing through the inductor is 0.4A at a frequency of 60Hz. What is the reactive power in the inductor?
3. A 0.5H inductor has a resistance of 150 ohms. The current flowing through the inductor is 0.4A at a frequency of 60Hz. What is the apparent power in the circuit

So basically in all three problems it has same inductor, same resistance and same current through it.
1. I found real power to be 24W ($V_L=0.4A \cdot 150ohms=60v$ then $Q=60V \cdot 0.4A=24W$ The reason I know its 24W because it was among the multiple choice answers but in my understanding the real power can only be dissipated by a Resistor, how in this problem inductor dissipates 24W of real power?
2. To find reactive power I'm not sure how to find that. By using power triangle, I only know 24W.
3. If i'll find out Real and Reactive powers i should be able to calculate Apparent power.

Please help me on this problem. Thank you.

2. ### Heavydoody Active Member

Jul 31, 2009
140
11
The problem specifies that the inductor has a resistance of 150 Ω. This is the real part of the inductor's impedance, disipating real power. BTW, real power is symbolized with P, not Q.
You must determine X, the imaginary part of the inductor's impedance Z (its reactance). This is defined as jωL. ω is found by $2 \times \pi \times f$. Reactive power is then $Q=I \small _{RMS}^2 \large \times X$
Apparent power (S) is the magnitude of the complex power (P+jQ).

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