[SOLVED] very basic question about phase in capacitor/inductors

Hello guys,

A very basic question about electronics regarding voltage/current phase in inductors and capacitor?

What is the physical reason of current be lagged (+90 degrees) from the voltage in capacitor?
What is the physical reason of current be leading (-90 degrees) from the voltage in inductors?

Thank you,

Consider a signal V = A sin wt.
Then the current through the capacitor is given by I = C dv/dt. Then I= -AC cos wt.

Now plot these two wave forms with time. You will clearly see that I reaches 0 only after a 90 degree. So current lags voltage

The current flowing through the inductor will be I = (1/L) * integration of voltage= A/L cos wt.

Now draw this graphically. You can clearly see that current seems to have reached the maximum in the beginning itself whereas voltage takes 90 degree to reach the maximum. Hence current leads voltage in inductors.


Hope this Helps.

Regards,
iVenky.

Alternating voltage and current in a capacitive circuit
Initially the voltage is zero and the capacitor is uncharged. In the first moments the current increases quickly. Later, as voltage is increasing the capacitor is charging and the closer the voltage gets to its peak, the slower it changes, meaning less current has to flow. And when the voltage reaches the peak , the capacitor is fully charged and the current is momentarily zero. Following the peak the circuit reverses and the charge leaves the capacitor, so the current always arrives at a certain point in the cycle 90 degrees ahead of the voltage, because of the charging and discharging action.
To better understand why this is need to consider relationship between voltage and charge for a capacitor: CV = Q and relationship between current and the flow of charge I= dQ/dt = C dV/dt ...

Capacitor current leads...

Paradoxical, isn't it?

One observation that demystifies it, is that the capacitor starts discharging at some point into the falling sinewave.

Capacitor current leading cannot occur with square waves.

I put a video on Youtube which demonstrates the capacitor-leads coil-lags effect. (Click link below.)

It graphically portrays changing voltage, direction and intensity of current flow, capacitor charge/discharge, and dynamics of the coil emf and flux field.

Cap Leads Coil Lags (Animated) - YouTube

Thanks, guys!

best regards,

The fundamental EletroMagnectic theory, says that doesn´t exists flowing current itself, or flowing voltage itself.
In fact, a V phenomen generates a I phenomen.

Electric waves are dephased on Magnectic waves by 90 degres.
It may be considered as a good way to understand.

**broken link removed**


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