Electrical Engineering - RL Circuits - Discussion

Discussion :: RL Circuits - General Questions (Q.No.3)


In a series RL circuit, 12 V rms is measured across the resistor, and 14 V rms is measured across the inductor. The peak value of the source voltage is

[A]. 18.4 V
[B]. 26.0 V
[C]. 2 V
[D]. 20 V

Answer: Option B


No answer description available for this question.

Samuel Amu said: (Feb 23, 2012)  
In a series circuit, current is constant. assume a unity current flowing in the cct., then XL=VL/I, nb I=1(assumed). XL=14/1=14
and R=VR/I=12. cct impedance Z=(R^2+XL^2)^(-2)
peak voltage: Vp=IZ
Vp=18.439 v

So answer is Option A.

Chris said: (Mar 22, 2012)  
Current can't be constant, its a AC signal. If so, Z(L) would be zero.
But option B isn't correct either cause RMS isn't the same as peak.

Gerald said: (Aug 29, 2012)  
The relationship between peak and rms voltages is given as: Vrms = (Vpeak)/sqrt(2).
As a continuation to Samuel Amu's solution, his answer (18.439V) is still the rms value.
Transforming to peak value gives:
Vpeak = (Vrms)*sqrt(2) = 18.439*sqrt(2) = 26.07 Volts.

D.P.Mishra said: (Jan 15, 2013)  

i.e sqrt12^2+14^2=sqrt340.


i.e Sqrt(2*340)=sqrt680=26.0V approx.

Pravin said: (Feb 17, 2014)  

Two voltage are connected in series so the two are addition so simple as this Que.

12+14 = 26.

Pavan said: (Apr 15, 2014)  
While taking RL load the relation ship can not be said by sqrt 2 times then rms value. Because for RL circuit V can be measured by Laplace which never in terms of Sin it will be exponential in nature which rms is not 1/sqrt 2.

otherwise answer is taken w.r.t. fundamental formula:

V = (12^2+14^2)^0.5.

Satisfies all condition.

Ashoka.J said: (Jan 14, 2015)  
In series circuit v = v1+v2.

So total volume is 12+14 = 26.

26/2 = 13.V, peak = 13*1.414 = 18.38 v.

Chaitanya said: (Jul 7, 2015)  
Sqrt(VL^2+VR^2) = Vrms.

i.e sqrt 12^2+14^2 = sqrt 340.

Vp = sqrt 2*Vrms.

i.e Sqrt(2*340) = sqrt 680 = 26.0 V approx.

Guesh Berhe said: (Aug 11, 2015)  
I am satisfied by this question.

Tejal said: (Oct 23, 2015)  
Two voltage are connected in series so the two are addition so simple as this question:

12+14 = 26.

But 12 and 14 are RMS values, n in Q? Asked peak value of source.

Thus peak values can be calculated from RMS values from the formula, which implies Vp = VRMS*2.

Answer is 36.7.

Khushbu said: (Jan 29, 2016)  

You should write srrt(2) instead of 2 answer is correct.

Karuna said: (Apr 29, 2016)  
Really, they asked the peak value. So, the answer is (12 + 14)1.414 = 36.764.

Asad said: (Sep 4, 2016)  
V = sqrt(Vr2 + Vl2),

V = sqrt(12 pow 2 +14 pow 2),

V = sqrt 340,

V = 18.43,

Vpeak = 18.43 x 1.41,

Vpeak = 26 volts.

Manish Sharma said: (Sep 1, 2018)  
26.00v is the correct answer.

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