I have problems calculating voltage and current in AC circuits.
The circuits: http://img238.echo.cx/img238/5515/ac0sl.gif
Can someone verify and tell me if this is correct? I am pretty shure about circuit 1 and 2, but not the third circuit.
My calculations for circuit:
1a.
f=159Hz
Xc=1/wc=10010ohm
I=sqrt(R^2+Xc^2) sqrt(10000^2+10010^2)=3,53*10^-4A
UR=I*R 3,53*10^-4*10000=3,53V
UC=I*1/wc 3,53*10^-4*10010=3,53V
U=sqrt(UC^2+UR^2)=5V
2a.
f=159Hz
Xc=10010ohm
I1=U/R 5/10000=5*10^-4A
I2=U/R 5/10010=5*10^-4A
I=I1+I2=10^-3A
3a.
f=159Hz
Xc=10010ohm
Replace the two resistors with: 1/10000+1/10000=1/ans=5000ohm
I=U/sqrt(R^2+(1/wc)^2) 5/sqrt(5000^2+10010^2)=4,47*10^-4A
U=I*R 4,47*10^-4*5000=2,235V
IR1=U/R 2,235/10000= 2,235*10^-4A
IC=U/(1/wc) 2,235/10010=2,23*10^-4A
Thanks in advance!
The last circuit is 2.5 volts and 5 kohms drivning the cap.
Ok, 2,5V=(5*10k)/(10k+10k)=U0
If the cap gets 2,5V then the resistor R1 also gets 2,5V because they are in parallel, right?
Then,
IR1=U/R 2,5/10000=2,5*10^-4A
IC=U/(1/wC) 2,5/10010=2,498*10^-4A
I=5/sqrt(5000^2+10010^2)=4,47*10^-4A
But I-IR1-IC does not match. What am I doing wrong here?
Quote from: PeterWhat am I doing wrong here?
The voltage over the capacitor is frequency dependent.
The circuit is only a resistor (5 kohms) and a cap.
The capacitor will get 2.5 volts across itself only at DC.
Compare the first circuit in your drawing.
I get,
I=2,5/sqrt(5000^2+10010^2)=2,23*10^-4A
The current will be the same in R and C because they are in serie.
Then,
UR=1,115V and UC=2,23V
Check the voltage sqrt(1,115^2+2,23^2)=2,5V
Seems to be correct. What do you think?
Thank you very much for your help peranders!
You're welcome. :D
Hint: Norton-Thevenin convertions may be very handy sometimes, also Y-D convertions so I recommend that you study those so you will know about them.