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Home » AC Fundamentals » Why Power is Zero (0), in Pure Inductive, Pure Capacitive or a circuit in which Current and Voltage are 90 Degree out of phase?

Why Power is Zero (0), in Pure Inductive, Pure Capacitive or a circuit in which Current and Voltage are 90 Degree out of phase?

Why Power is Zero (0), in Pure Inductive, Pure Capacitive or a circuit in which Current and Voltage are 90 Degree out of phase?

1.  Why Power in a circuit is Zero (0), in which Current and Voltage are 90 Degree out of phase?

If Current and Voltage are 90 Degree Out of Phase, Then The Power (P) will be zero. The reason is that,
We know that Power in AC Circuit
P= V I Cos φ
if angle between current and Voltage are 90 ( φ = 90) Degree. then
Power P = V I Cos ( 90) = 0
[ Note that Cos (90) = 0]
So if you put Cos 90 = 0→Then Power will be Zero (In pure Inductive circuit)

2.  Why Power in pure Inductive Circuit is Zero (0).
We know that in Pure inductive circuit, current is lagging by 90 degree from voltage ( in other words, Voltage is leading 90 Degree from current) i.e the pahse difference between current and voltage is 90 degree.
So  If Current and Voltage are 90 Degree Out of Phase, Then The Power (P) will be zero. The reason is that,
We know that Power in AC Circuit
P= V I Cos φ
if angle between current and Voltage are 90 ( φ = 90) Degree. then
Power P = V I Cos ( 90) = 0
[ Note that Cos (90) = 0]So if you put Cos 90 = 0→Then Power will be Zero (In pure Inductive circuit)
                                                             Click image to enlarge

3.  Why Power in pure Capacitive Circuit is Zero (0)?
We know that in Pure capacitive circuit, current is leading by 90 degree from voltage ( in other words, Voltage is lagging 90 Degree from current) i.e the phase difference between current and voltage is 90 degree.
So  If Current and Voltage are 90 Degree Out of Phase, Then The Power (P) will be zero. The reason is that,
We know that Power in AC Circuit
P= V I Cos φ
if angle between current and Voltage are 90 ( φ = 90) Degree. then
Power P = V I Cos ( 90) = 0
[ Note that Cos (90) = 0]So if you put Cos 90 = 0→Then Power will be Zero (In pure capacitive circuit)

                                                              Click image to enlarge

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11 comments

  1. what is difference between capicitance(C) and capacitor reactances(Xc)????<br />plz ans

    • Capacitance = the ability of a body to store an electrical charge<br />C = Q/V<br />and<br />Capacitive reactance = an opposition to the change of voltage across an element.<br />its a type of resistance in AC circuit.<br />Xc = XC= 1/2πfC

  2. please ans me we say capictor is use for improve power factor but the prove is reciprocal

  3. please ans me we say capictor is use for improve power factor but the prove is reciprocal

  4. thank you. very useful<br />

  5. what is the concept of lagging by 90 degree leading by 90 degree in cpacitor and an inductor?pls ans…..<br />

  6. plz tell me we know that current decrease when value of resistor in a circuit increases so then why electric heater draw max current instead of having max resistance..

    • Current Decreases??… Obviously, because the resistance opposes the current to flow. but it not means that there is no flow of electron. Did you hear about Joule’s law… P = I^2Rt as well as Heating effect of current in the conductor ?? that is the answer.

  7. Onarinde John Babatunde

    How can I have the pdf or miocrosoft word format of the Basic Electrical Engineering Questions and Answers?

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