Hi.
I am preparing electrial exam for 2330 Level2
I have a question about power factor.
"the power factor of resistive and inductive circuit having an mpedance of 1 ohm and resistance of 0.6 ohm is....?"
1) 0.8 leading
2) 0.6 leading
3) 0.8 lagging
4) 0.6 lagging
the answer is 0.6 lagging, but I don't understand how the answer comes.
also need some explanation about the definition about "impedance"
cheers
I am preparing electrial exam for 2330 Level2
I have a question about power factor.
"the power factor of resistive and inductive circuit having an mpedance of 1 ohm and resistance of 0.6 ohm is....?"
1) 0.8 leading
2) 0.6 leading
3) 0.8 lagging
4) 0.6 lagging
the answer is 0.6 lagging, but I don't understand how the answer comes.
also need some explanation about the definition about "impedance"
cheers
-
If you want to learn about electrical impedance, you will need to read up on its definition. It is somewhat complicated and involves complex arithmentic. To cut to the chase, impedance is the combination of resistance (from a resistor) and reactance (from an inductor or a capacitor, positive and lagging if an inductor, negative and leading if a capacitor). Resistance and reactance act vectorially as if they are at right angles to each other. They form a right triangle where impedance (Z) is the hypotenuse, resistance (R) and reactance (X) form the legs. So to achieve a Z of 1 and an R of .6, the X must be .8 since this is similar to a 3-4-5 right triangle. Mathematically:
Z^2 = R^2 + X^2
where Z, R, and X are expressed in ohms.
Note the 1^2 = 0.6^2 + 0.8^2
Where does leading and lagging come from? It a description of what the current waveform does relative to the voltage waveform. The pneumonic for remembering this is:
ELI the ICEman
If it's an inductor (L), voltage comes first, so *current is Lagging*
If it's a capacitor (C), current comes first, so *current is Leading*
(E = voltage, I = current, L = inductive, C = capacitive)
Or just try to remember, and inductive circuit or inductive current is alway lagging.
As for power factor, that is the ratio of power to apparent power. It works out such that it is also the ratio of resistance to impedance, since the impedance triangle is the same shape as the power triangle. The power factor is therefore:
PF = R/Z = 0.6/1.0 = 0.6
Add the "lagging" since the circuit is inductive.
PF = 0.6 lagging <=== Answer.
Z^2 = R^2 + X^2
where Z, R, and X are expressed in ohms.
Note the 1^2 = 0.6^2 + 0.8^2
Where does leading and lagging come from? It a description of what the current waveform does relative to the voltage waveform. The pneumonic for remembering this is:
ELI the ICEman
If it's an inductor (L), voltage comes first, so *current is Lagging*
If it's a capacitor (C), current comes first, so *current is Leading*
(E = voltage, I = current, L = inductive, C = capacitive)
Or just try to remember, and inductive circuit or inductive current is alway lagging.
As for power factor, that is the ratio of power to apparent power. It works out such that it is also the ratio of resistance to impedance, since the impedance triangle is the same shape as the power triangle. The power factor is therefore:
PF = R/Z = 0.6/1.0 = 0.6
Add the "lagging" since the circuit is inductive.
PF = 0.6 lagging <=== Answer.