PSN-L Email List Message

Subject: Re: Question
From: Karl Cunningham karlc@..........
Date: Sun, 12 Dec 2010 09:47:44 -0800


Geoffrey,

It's still 90 degrees. When you have components in series (any kind of 
components) the current through all of them is equal, including the 
phase of that current.

One way to look at how capacitors work is that the voltage across the 
capacitor is the result of past current through it. The current is what 
puts charge into the capacitor. And there is voltage across the 
capacitor because it is holding charge.

True, the current leads the voltage. But another way to look at it is 
that the voltage (which is due to the accumulated charge) lags the 
current (which is what's putting the charge in) by 90 degrees.

Karl


Geoffrey wrote:
> Hello PSN;
> 
> Im trying to build an N=8 LP_filter for 10Hz
> and in one or more of the stages I
> need a 0.5uf capacitor.
> 
> 
> It seems easy enough.
> 
> Got lots of 1uf from past projects.
> 
> Like some kind of electronics Vulture, want to scavenge those.
> 
> So.
> 
> I thought Id just put two 1.0u in series
> to get a single one with a 0.5u value.
> 
> 
> Well that sounds fine but I got a question about phase shifting.
> 
> Eli the Ice man tells me that in a condenser the current leads the
> voltage by 90 degrees across a capacitor.
> 
> 
> Well then, if you put two in series
> does that mean the shift is now 180 degrees ?
> 
> To go further, It says 90 in the swcad program
> which I'm still not sure about.
> 
> 
> Anyone know 100% for sure
> what the ideal phase shift is across
> two condensers in series ?
> 
> Geoff
> 
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