- #1

tim_lou

- 682

- 1

Basically, we set up a function generator, and measure voltage output using oscilloscope.

We set up a circuit with an inductor-capacitor in parallel, then the whole thing in series with a resistor.

we measure the amplitude of the input and output (across resistor) voltage while varying the frequency.

according to the mathematics, the ratio between output and input squared should be:

[tex]G^2=\frac{R^2}{R^2+(\omega L-\frac{1}{\omega C})^{-2}}[/tex]

so that when,

[tex]\omega=\frac{1}{\sqrt{LC}}[/tex]

the ratio goes to zero. and around that region, there is a spike. basically, G is pretty much constant (around 1) and shoots vertically down around notch frequency (which is what we tried to find out).

the resistance is 1k ohm

capacitance is .1 micro-Farad

inductance is 1 mili-Henry

the theoretical notch frequency is around 15.9kHz. However, the result turned out to be around 17.5kHz. the weird thing is, not only did my group get off-results, all the people I asked got the same! around 17.5 kHz. and I checked and checked... the theory should be correct!

furthermore, the slope of the spike is much gentler as well... in theory, it should be really really sharp (at least 100 times "sharper" or "narrower")

what has gone wrong? is something wrong with the equation? I think it might've been internal resistance but how could it have such a tremendous effects?

Anyone got any idea?