Electrical Engineering - RC Circuits - Discussion

Discussion :: RC Circuits - General Questions (Q.No.23)

23. 

A 120 resistor is in parallel with a capacitor with a capacitive reactance of 40 . Both components are across a 12 V ac source. What is the magnitude of the total impedance?

[A]. 37.9
[B]. 3.7
[C]. 14,400
[D]. 4,800

Answer: Option A

Explanation:

No answer description available for this question.

Jeyanand Nec said: (Mar 9, 2012)  
Z=1/Y

Y=(1/R)+(j/Xc)

=sqr(0.0083^2+0.025^2)

=0.02634 mho

Z=1/0.02634=37.9 ohms

Towqeer said: (Sep 8, 2012)  
Sorry! i'm not getting this....why u solve through Admittance__as we have to find impedance then why not to solve through: Z=sqrt R^2 + Xc ^2 _even we got through this wrong answer.
and by ur method ..answer is right...but i want to the Logic..plz !!

Preplexed said: (Oct 2, 2012)  
Is it a convention to solve such questions through Admittances? Can I have the reasoning behind it please?

Dilip Verma said: (Sep 7, 2013)  
Because it is in parallel rc circuit so Ir = V/R = 12/120 = 0.1 and Ic = 12/40 = 0.3

So I = root(Ir2+Ic2) = root.1 = 0.31622.

Z = V/I = 12/.316 = 37.9

Rakesh Devaraj said: (Sep 26, 2014)  
@RAKESH DEVARAJ.

WE NOW THAT Z = sqrt(R^2+XC^2) .
FOR PARALLEL Z = 1/(sqrt(1/R^2+XC^2)).

So z=1/(sqrt(1/120^2+1/40^2)).

z=37.94 Ohm.

Beder B said: (Jan 28, 2015)  
Zr = 120.

Zc = j(XL-Xc) and XL = 0 and Xc = 40 therefore Zc = -j40.

1/Zeq = 1/Zr+1/Zc = 1/120+1/-j40 = (120-j40)/(-j4800).

Zeq = (-j4800)/(120-j40).

Multiply by (120+j40)/(120+j40).

Zeq = (192000 - j576000)/16000.

Simplify,

Zeq = 12-j36.

|Zeq| = sqrt((12^2)+(36^2) = 37.9.

Parneet Kaur said: (Jul 11, 2015)  
If in case of parallel RC circuit all the parameters are like 1/z and 1/r then why 1 /xc is not done.

Sudhir said: (Apr 8, 2016)  
Znet=(R*jXc)/R-jXc

Solve by substituting the value.

R!Tesh said: (Jun 8, 2016)  
sqrt(1/Z) = sqrt(1/r) + sqrt(1/Xc).

1/Z = sqrt((1/120)^2 + (1/40)^2).

1/Z = 0.0263.

Z = 37.94.

Raza said: (Nov 2, 2018)  
Impedence in perallel is = z = RXc /√ R^2+Xc^2.

Post your comments here:

Name *:

Email   : (optional)

» Your comments will be displayed only after manual approval.