J
J. Payne
Guest
For a physics project I set up the following circuit:
_________
| < R1(=1Meg)
~Vs >
| |
| =C1(=22pF)
|_________|
I was just running a test run with a real capacitor before what I
intended to do, which was to measure the capacitance between two
parrallell wires.
Anyway, I varied the frequency of Vs (which I kept at a constant
voltage) and measured the voltage across C1. If my calculations are
correct (and I checked them a lot), then this voltage should equal:
Vs(1/(2*pi*R1*f*C1+1))
I also plotted the recipricol of this as a graph. What I was expecting
was a straight line passing through 1/Vs on the y axis with a gradient
of (2*pi*R*C)/Vs. What I got however, was not straight, but had a
decreasing gradient like this:
|V
|
| _______
| /
| /
|/_________________f
well, not quite that extreme.
What explanation would there be for this, as I know wish to maybe
study this phenomenon instead (rather than the cap between wires).
--JP
(PS I tried modelling this in spice but instead of a straight line or
line like I got, I got a line with increasing gradient - unless I used
the magnitude of the complex number I was given)
_________
| < R1(=1Meg)
~Vs >
| |
| =C1(=22pF)
|_________|
I was just running a test run with a real capacitor before what I
intended to do, which was to measure the capacitance between two
parrallell wires.
Anyway, I varied the frequency of Vs (which I kept at a constant
voltage) and measured the voltage across C1. If my calculations are
correct (and I checked them a lot), then this voltage should equal:
Vs(1/(2*pi*R1*f*C1+1))
I also plotted the recipricol of this as a graph. What I was expecting
was a straight line passing through 1/Vs on the y axis with a gradient
of (2*pi*R*C)/Vs. What I got however, was not straight, but had a
decreasing gradient like this:
|V
|
| _______
| /
| /
|/_________________f
well, not quite that extreme.
What explanation would there be for this, as I know wish to maybe
study this phenomenon instead (rather than the cap between wires).
--JP
(PS I tried modelling this in spice but instead of a straight line or
line like I got, I got a line with increasing gradient - unless I used
the magnitude of the complex number I was given)