Help with problem 7.26 please.

Thread Starter

thisonedude

Joined Apr 20, 2014
52
My Impedance, from what i calculated, was 20+40j. I know power is V^2/2R. and my w = 2pi(400) = 800pi. Can i get some help?
 

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shteii01

Joined Feb 19, 2010
4,644
Power=V*I
I=V/R
Power=V*(V/R)=(V^2)/R

Conclusion: You don't know power.


Also. Since you have current source, you are better of using current to find power:
Power=V*I
V=I*R
Power=(I*R)*I=R*I^2
This way you know the Equvalent Impedance of the circuit (R=20.166+40.124j) and you know the Current since it is given by the problem.
 
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Thread Starter

thisonedude

Joined Apr 20, 2014
52
so if my impedence is 20+40j. And my current is 10cos(wt+27°) = 10e^(j27°). so then my current^2 is 100e^2(j27°) and my power is (20+40j)(100e^2(27°)) Does this seem/sound right?
 

shteii01

Joined Feb 19, 2010
4,644
so if my impedence is 20+40j. And my current is 10cos(wt+27°) = 10e^(j27°). so then my current^2 is 100e^2(j27°) and my power is (20+40j)(100e^2(27°)) Does this seem/sound right?
10e^(j27°) this is Phasor Representation.

You have three choices:
* Time domain
* Phasor
* Complex

10cos(wt+27°) is Time domain

10e^(j27°) is Phasor

Complex is 10*cos(27°)+j*10*sin(27°) Once you find cos and sin, you will have current in the form of complex number (X+jY). So now the form that represents current matches the form that represents impedance. Since they are in the same form, you can do math with them.
 

Thread Starter

thisonedude

Joined Apr 20, 2014
52
Oh i see. So then if i do the math, my current is 8.91+j4.5. if i square this, i get 58.86+80.72j. So then i muliply that by 20+j40?
 
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