how power can be calculated

plz tell me how can i calculate Volatge (rms) from peak value of voltage . how can the KWH be calculated using power formula (V*I). how one unit drops in electric meter . i have value of current and voltage how i can calculate apparent and true power and how KHW can be calculated from voltage and current value .

rms voltage is found by multiplying the peak value by 0.707 (approx for 1/sqrt(2)).

KWH cannot be found with simply V and I. A KWH is found by multiplying watts by the time the device is in use.

See link for def of apparent power.
**broken link removed**

V(rms) = Vpeak/√2 if the voltage is a sine wave.
Otherwise you'll have to integrate and find out.
V(rms)=√[∫{V(t)²}/T]

Now if voltage and current are both complex numbers then power S is given by
S=P+jQ = V.I* where P is the active power and Q is reactive power and I* stands for conjugate of I.
KWH is calculated by active power multiplied by the time for which it is drawn.

Voltage RMS is calculated like this:
Vrms=Vpk/√2

The apparent power is simply S=Vrms*Irms

The 'true' power is P=Vrms*Irms*cosφ, where φ is the phase shift angle between voltage and current.

If the voltage and current are in phase, then P=S.

If you want to calculate the energy [kWh] then you simply multiply P by the time.

Apparent Power (VA) is the product of the RMS Current and the RMS voltage.

True power is the time integral of the (product of instantaneous current and instantaneous voltage) divided by the time period.

Energy (KWH) is the same as above, except that the integration is over an indefinite period of time, and you don't divide by a time interval. If you're working with Volts, Amperes and seconds, then you must multiply the result by:
~ (.001KW/Watt)(1/3600 Hours/Sec) to get KWH. A KWH meter performs this integration.
.
For sine waves, the calculation of reactive power and true power is simpified.
Pr = VIsin(Theta)
Pt = VIcos(Theta)
Pa = VI
Where
. V = RMS Voltage
. I = RMS Current
. Theta = phase angle between voltage and current.
. Cos(Theta) is the power factor (PF).
. In general, PF = (True power)/(Apparent Power)
Regards,
Kral