# Calculating power and Impedance

Discussion in 'Homework Help' started by regexp, Dec 21, 2010.

1. ### regexp Thread Starter New Member

Nov 20, 2010
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0
Hi,

One part of this question, i am uncertain of.

"The current and Voltage through an impedance are known"
$u(t) = \sqrt2\cdot110cos(\omega t+85)V$
$i(t) = \sqrt2\cdot0.4cos(\omega t+15)A$

Calculate the power and reactive power in the impedance.

The powerangle is 70°
So we have $V_{rms} \cdot I_{rms} \cdot cos 70^\circ= 15A$
and $V_{rms} \cdot I_{rms} \cdot sin 70^\circ = 41.34VA$

"Calculate the apparent power in the impedance"

Apparent power = $V_{rms} \cdot I_{rms} = 44$

"Calculate the impedance Z"

Not sure about this one, is it simply 110/0.4 = 275Ω ?

Last edited: Dec 21, 2010

Nov 25, 2009
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3. ### regexp Thread Starter New Member

Nov 20, 2010
24
0
Second try.

Power P = $V_{rms} \cdot I_{rms} cos(\theta)$

Reactive power Q = $V_{rms} \cdot I_{rms} sin(\theta)$

Apparent power S = IE(being the same as V_rms x I_rms)?

4. ### Georacer Moderator

Nov 25, 2009
5,142
1,266
That's what I would write too. But since power electronics is not my forte, I 'd like someone else to confirm it.