RC low pass filter?

We did preform an experiment in university lab:
Peak voltages are 5v
Capacitor Value: 1micoFarad
Resistor: 1.8k
Calculated Critical frequency as per given data is: 93c/s (getting voltages on Oscilloscope is 2.4 volts which is 70% of the input voltages)
Questions is that, when we increase the frequency of voltages approximately about 3000c/s or above, then the input voltages varies and going down from 3.5peak volts to 2.9 and so on on the next frequencies. Can any one please explain this how to perform this experiment precisely?

Hi,

Well you see, frequency and voltage has an indirected relationship. If you can recall, V(t) = Vp*sin(w*t) = Va*sin(2*pi*f*t)
where:
V(t) = the instantaneous voltage at any time t
Vp = peak voltage value (i.e. "amplitude")
f = frequency of the AC signal (hertz or cycles/sec)
w = angular frequency (radians/sec) = 2*pi*f
t = 1/f = period of one oscillation

I am not exactly sure what are the objective and parameters being ask in that experiment, but I hope its clear to you what is the relationship of the variables here.

I hope this helps,
Kevin

Thankyou ever so much it solved half of my problem!. So you meant, if we need to supply constant voltage of 3.5 peak, then we must increase the voltage with respect to frequency to overcome this drawback in the voltage that comes in 3.5 volts?

f=1/2piRC