# Electrical Engineering - RLC Circuits and Resonance - Discussion

Discussion Forum : RLC Circuits and Resonance - General Questions (Q.No. 1)
1.
A 10 resistor, a 90 mH coil, and a 0.015 F capacitor are in series across an ac source. The impedance magnitude at 1,200 Hz below fr is
1,616 161 3,387 1,771 Explanation:
No answer description is available. Let's discuss.
Discussion:
25 comments Page 1 of 3.

Usman Asif NFC said:   3 years ago
Following Value given:
R= 10 ohm.
L= 90mH.
f=1200 Hz.

Impedance Formula: Z = √ ( R^2 + (X.L - X.C)^2).

We have value of "R" Now find X.L & X.C

X.L = wL Where as (w: ω = 2*π*f*L).
X.C = 1/w.C.

frequency = 1/ (2*π*L*C).

Now put all the required values in Z = √( R^2 + (X.L - X.C)^2).
(1)

AGGREY KERE said:   9 years ago
From R-L-C circuit above, we know that; Z=root of R^2+(XL-XC)^2.
but XL=2pi*fr*L.
XC=1/2Pi*fr*C.

We know that formula for Impedence(Z)
Z=Sqr root of (R^2+(Xl-Xc)^2)
Here R=Resistance
Xl=wl (w=2*3.14*f) and l=inductance of a coil
Xc=1/wc Here c=capacitance of capaciter

Z=Sqr root of (R^2+(Xl-Xc)^2)

Azeem said:   3 years ago
As the given frequency is 1200 Hz less than fr(resonance).

Frequency = fr-1200
Fr= 1/2*π√LC.
fr= 4331.

Frequency = f = 4331-1200 = 3131 Hz.
Z= √R^2 + ( Xl-Xc)^2.
Z= 1616.
(4)

ROBERT said:   8 years ago
XL=2*3.14*F*L THIS IS THE FORMAL.

I WAS ASK TO MAKE SO I CAN FIND UNKNOWN F AND L.

MOVE THING AROUND I CAME UP WITH SO ARE THESE RIGHT.

F=2*PI*L*XL.
L=2*PI*F*XL.

Manindra said:   9 years ago
Fr = 1/2*pi*sqrt(L*c)=4331.648.
f = fr-1200Hz = 3131.64.

Xl = Wl = 2*3.14*3131.64*l.

Xc = 1/wc.
Z = sqrt of(R^2+(XL-XC)^2) = 1616 ohm.

Rajat Dey said:   8 years ago
I know above formula but this is very long process and heavy time span. So how can do it quickly? Please help me.

XL=WL=(2*PI*f)L
XC=1/WC=1/(2*PI*f)C
where,L=90mh,C=.015microF, f=1200hz and R=10ohm

Z=sqrt of(R^2+(XL-XC)^2)

Mrakovic said:   9 years ago
fr = 1/2*pi*sqrt of LC.
fr = 4331.648.

f = fr-1200Hz=3131.64.
Z = sqrt of(R^2+(XL-XC)^2).

Z = 1617 ohm.

Prashant said:   8 years ago
I think result is not coming from above all formula I want real answer from you friends please reply.