# AC power calculations:

Discussion in 'Homework Help' started by whynotsneeze?, Nov 9, 2009.

1. ### whynotsneeze? Thread Starter New Member

Nov 6, 2009
2
0
Hi, im a bit lost with AC circuits on the whole and could use some dumbed down explanation on the matter.

Taking an example from course material:

(Components connected in parallel. "Ladder connection")

------
l l l l l
J C L R
l l l l l
------

Where
J = 1 (30 degrees) currentsource driving current in the clockwise direction
C = 0.05 F capacitor
L = 0,2 H inductor
w = 10 rad/s

If im asked to find the real and reactive powers for each component how would i go about solving these?
I could also use a clarification on the difference between real and reactive powers.

Thanks.

ps: sory for the dingy "diagram"

2. ### mik3 Senior Member

Feb 4, 2008
4,846
63
Find the current through each component according to their impedance which for C and L depends on the current source frequency. C and L have only reactive power, use their impedance value and calculate it like the power in a resistor. The only real power is dissipated in the resistor. This is if the L, C, R and J are ideal.

3. ### Thav Member

Oct 13, 2009
82
0
I started to explain this but it is very difficult to explain concisely. To solve your problem you will have to know about complex impedances and AC analysis. (hint here: the complex impedance of the L and C are functions of j (the imaginary number), w and L and C respectively). You will also find phasor notation of complex numbers helpful.

Chapters 2-5 should be most of what you need to know.

4. ### Thav Member

Oct 13, 2009
82
0
Also in response to mik3, it's not a given that the current source J will not deliver any reactive power, it just happens to be so in this case.

5. ### mik3 Senior Member

Feb 4, 2008
4,846
63
Complex impedance maybe be the easiest way to solve it but if he feels better with differential equations, that is fine.