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Kirt Blattenberger,
BSEE
 KB3UON
RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The Internet was still largely an unknown entity at the time and not much was available in the form of WYSIWYG ...
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Power factor measures the phase angle between the instantaneous voltage and the instantaneous current in a circuit. Voltage (E) leads current (I) by 90° in an inductive (L) circuit and voltage (E) lags current (I) by 90° in a capacitive (C) circuit.
A popular mnemonic is ELI the ICE man since E is leading (coming before) I in ELI, and E is lagging (coming after) I in ICE.
power factor ( P_{f} ) = cos ( q ) 

Apparent Power ( P ) = I * V  
True Power = P  
I = Current  
q = Phase angle  
V = Voltage 
Power Formulas  
Apparent Power P = I * V P = I^{2} * R P = V^{2} / R 
True Power P = I * V * cos (q) P = I^{2} * Z * cos (q) P = V^{2} * cos (q) / Z P = P_{a} * P_{f} 
Impedance Z = V^{2} * cos (q) / P Z = P / [I^{2} * cos (q)] 

Current I = P / [V * cos (q)] I = sqrt {P / [Z * cos (q)]} 
Voltage V = P / [I * cos (q)] V = sqrt [P * Z / cos (q)] 

