Electrical Engineering - Circuit Theorems and Conversions - Discussion

Discussion :: Circuit Theorems and Conversions - General Questions (Q.No.11)

11. 

What is the Thevenin equivalent (VTH and RTH) for the circuit given?

[A]. 6.4 V, 422
[B]. 6.4 V, 560
[C]. 6.4 V, 680
[D]. 30 V, 422

Answer: Option A

Explanation:

No answer description available for this question.

M.V.Krishna/Palvoncha said: (Dec 19, 2011)  
From the circuit

Vth= ((R1||R3)*Vs)/(R1+R3);

(note: R1||R3 means R1 in parllel with R3, R1||R3=149.8);

on sloving we get

Vth=(149.8*30)/690

Vth=6.5 (app. equal to 6.4v;

from the circuit we get

Rth=(R1+R3)||(R2+R4)

Rth=690||1240;

Rth=443.31(app. equal to 422 ohm)

so option A

Praveen Juturu said: (Dec 9, 2013)  
Thevenin's resistance is (R1 // R2) + ( R3 // R4).

Thevenin's voltage is obtained by applying potential divider rule,

Vth = Voltage across R2 - voltage across R4.

Subarna Das said: (Jul 2, 2014)  
Vth = {30*(470/470+560)}-{30*(220/220+680)}.
Vth = 6.3V.

Rth = (470+220)//(680+560).
Rth = 443 ohm.

So, option 1 is right.

Shashi said: (Jan 10, 2015)  
R1 parallel to R2& R3 is parallel to R4 and the result of R1||R2&R3||R4 are in series.

= 220||680+470||560 = 421.75 (422).

Naveedabanu said: (May 26, 2015)  
I agree with answers. But I am not getting series and parallel combination. Please tell me if you know.

Nami said: (Nov 1, 2015)  
What about vth then?

Aswathy said: (Jul 23, 2016)  
Rth = (R1 // R2) + ( R3 // R4).
= 220||680 + 470||560 = 421.75 (422).

Vth is the open circuited voltage therefore find the effective resistance neglecting RL
R eff = R1 + R2 II R3 + R4.
= 220 + 680 II 560 + 470 = 900 II 1030= (900 * 1030) /(900 + 1030) = 480.31.

Now find the total current.
I = V/Reff =30/480.31 = 0.062.

Find current through each parallel branch using current division:
I1 = (0.062 * 1030)/(1030 + 900) = 0.033.
I2 = 0.062 - 0.033 = 0.029.

Vth= VA - VB = V470 - V220.
=(470 * 0.029) - (220 * 0.033) = 6.37 v.

Akhila said: (Jul 26, 2016)  
Well said, Thank you all.

Shan said: (Jan 6, 2017)  
Vth is 6.28.

Use vlt divider rule.

Prashant said: (Aug 9, 2017)  
Thanks @Aswathy.

Pkgp said: (Dec 13, 2018)  
Thank you all.

Praveen said: (Jun 19, 2019)  
Thanks for explaining it.

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