Electrical Engineering - Circuit Theorems and Conversions - Discussion

Discussion :: Circuit Theorems and Conversions - General Questions (Q.No.1)

1. 

Find the Thevenin equivalent (VTH and RTH) between terminals A and B of the circuit given below.

[A]. 4.16 V, 120
[B]. 41.6 V, 120
[C]. 4.16 V, 70
[D]. 41.67 V, 70

Answer: Option D

Explanation:

No answer description available for this question.

Pinvikesh said: (Dec 10, 2010)  
I am not getting answer for it and I also want the simplest way to do these problems of each modle to save time please send me and also your site is useful for alot us

Arasu said: (Jan 4, 2011)  
I want some simple technic for this sum.

Apuelectrical said: (Feb 18, 2011)  
rth = r3||(r1 + r2)

vth = vs.r3/r1+r2

Swetapadma said: (Jul 3, 2011)  
rth=120//(100+68)
vth=

vth = vs.r3/r1+r2
=ioo*120/(100+120+68)

Pabitra Roy said: (Sep 13, 2011)  
Vth=v*120/288,

Rth=168*120/(120+168)

Soma said: (Sep 17, 2011)  
Vth = R3*(Vs/(R1+R2+R3))= 120*(100/(68+100+120)) = 41.67 V

Rth = R3//(R1+R2) = (120*160) / (120 + 168)= 70 ohm

M.V.Krishna/Palvoncha said: (Dec 18, 2011)  
From circuit

Vth=VR3/(R1+R2+R3);Rth=(R1+R2)//R3;

on solving ans is option D.

N.Vinoth Kumar said: (Jan 30, 2012)  
R1+R2+R3=R

I=V/R

Vth=IR

Rth= (R1+R2)/R3

Sourav Sau said: (Feb 14, 2012)  
By voltage devider rule Vth= 120*100/68+100+120
Nd Rth= (R1+R2)//R3

Sumit Mathur said: (Feb 18, 2012)  
By voltage rule vth = 120*100/(68+100+120)=41.66
rth=120+100//68=70 ohm

Basavaraj K T said: (Feb 23, 2012)  
vth=(VS*R3)/(R1+R2+R3)
Rth=R1R2/(R1+R2)

Christan said: (Apr 25, 2012)  
Vth= VS*R3/(R1+R2+R3)
Vth= 120*100/(68+100+120)
Vth= 41.67 V

Rth= R3*(R1+R2)/(R1+R2+R3)
Rth= 120*(68+100)/(68+100+120)
Rth= 120*168/288
Rth= 20160/288
Rth= 70 Ohms

Kusuma said: (Jun 14, 2012)  
The resistances 68 and 100 are in series ; 68+100=168.

168 ohms is in parallel with 120 ohms. So,

Ith = (168*120) / (168+120) = 70 ohms.

Vth = R3* (Vs/R1+R2+R3).

Vth = 41.67V.

Loukya said: (Aug 27, 2012)  
vs=R3*V/(R1+R2+R3)
Vs=46.7
Rth=R3(R1+R2)/R1+R2+R3
Rth=70

Shivendra Soni said: (Apr 5, 2013)  
Rth = (R1+R2)II(R3)
= (68+100)II(120)
= 70 ohm.

Vth = I (loop current)*R3
= [Vs/(R1+R2+R3)]*R3
= (100/288)*120
= 0.347*120
= 41.67V.

Smritimoy said: (Jun 10, 2013)  
RTH = 68 + 100 = 168 ohm.

VTH = 100 v.

Saleem Shah said: (Jun 22, 2013)  
Rth = R3(R1+R2)/(R1+R2+R3).

Rth = 120(68+100)/(68+100+120).

Rth = 120*168/288.

Rth = 20160/288.

Rth = 70 ohm.

Vth = Vs*R3/(R1+R2+R3).

Vth = 100*120/68+100+120.

Vth = 12000/288.

Vth = 41.6 v.

Prafull Gadekar said: (Sep 23, 2013)  
Total Resistance,

Rt=R1+R2+R3=120+68+100 = 288ohm.

I = V/R = 100/288 = 0.347A(flowing same current in all resistance).

Now, we want to find voltage across R3=120 ohm.

V = 120*0.347 = 41.67V

Now, Rth = R3//(R1+R2) = 70 ohm.

Keerthana said: (Oct 13, 2013)  
1. Find Open Circuit Voltage(Vth):

Req = 68+100+120 = 288v.

Ieq = V/Req = 100/288 = .34722 A.

Voc =100-(68*.344722)-(100*.34722).

We get Vth = Voc = 41.667v.

Isc = 100/(68+100)= 0.5952A.

Rth = Vth/Isc.

Rth = 41.667/.5952 = 70 ohm.

Anirban Sengupta said: (Dec 29, 2013)  
Sorry, but I am not convinced with the explanation. Whenever we will find Rth, then we have to remove the load resistance completely and then we will find the Rth. Load resistance will not have any impact in it. Then please explain how Rth becomes 70?

Ayushi said: (Jul 15, 2014)  
Actually your doubt is common one, which usually strikes the mind anirban but R3 is not the load resistance infact the load is on a b terminal, and the load is not shown at the terminals. So the answer given that is 70 is correct.

Maheshwaran said: (Oct 1, 2014)  
Vth = R3*(Vs/(R1+R2+R3))= 120*(100/(68+100+120)) = 41.67 V.

Rth = R3//(R1+R2) = (120*160) / (120 + 168)= 70 ohm.

Akshit Raulji said: (Jan 7, 2015)  
First of all open 120 ohm resistance because Vth is find across it so it should be open than applied voltage divider rule.

Vth = 100*68/(68+100). So we get 40.47v.

K.Hanumantha said: (Feb 2, 2015)  
Friends.

According to Thevenin theorem voltage should be short while calculating of resistor Rth, when we do that, R3 is parallel with (r1+r2). So equivalent, 168//100 = 70 ohm Rth.

Vth = r3*I. where I = Vs/(r1+r2+r3) = 100/(68+100+120) = 0.3472A.

We need Vth = I*r3 = 0.3472*120 = 41.67V.

Khinya Ram Choudhary said: (Feb 16, 2015)  
Let R = R1+R2;

Rth = R||R3;

According to Thevenin Theorem:

Rth = (168*120/(168+120)) = 70 Ohm.

Vth is Thevenin voltage Between A&B,

According to Voltage Divider Rule:

Vth = Vs*R3/ (R+R3).

= 41.67 V.

Thangam said: (Jul 9, 2015)  
I need simple formula for solving these circuit analysis.

Prabha said: (Aug 1, 2015)  
I can't understand.

Anshu said: (Dec 30, 2015)  
When we have to find the venin voltage b/w two terminal then, firstly we have to remove the load resistance b/w these terminal. So why all are considering r3?

Naveen said: (Feb 5, 2016)  
Rth = 168.
Vth = 100 V.

Aaron said: (Feb 19, 2016)  
In what world is R3 parallel to R1 and R2? they look in series to me. It is parallel to the load yet, but not with R1 and R2. The definition of parallel connection is that it shares two or more nodes, and this simply does not. I am confused.

T.Ramachandran said: (Mar 28, 2016)  
Vth = the voltage across the 120 Ohms. this is calculated by determining the current in the loop by applying KVL.

The KVL in the loop is,

100 - 68I - 100I - 120I = 0
=> 100 = 68I + 100I + 120I
=> I = 100/288
=> I = 0.347A

and,

Vth = 120 * I
Vth = 120 * 0.347 = 41.67V

To find Rth,

68 and 100 in series and this series combination come in parallel with 120 Ohms.

So,

Rth = (168*120/168+120)
Rth = 58.33 Ohms.

Nagesh said: (Jul 23, 2016)  
The resistances 68 and 100 are in series ; 68 + 100 = 168.

168 ohms is in parallel with 120 ohms. So,

Rth = (168 * 120) / (168 + 120) = 70 ohms.
Vth = R3 * (Vs/R1 + R2 + R3).
Vth = 41.67V.

Rajiv Singh said: (Nov 7, 2016)  
Using voltage dider rule(vth) = 100 * 120/(60 + 100 + 120) = 41.66.
And rth = (100 + 68)/(100 + 68 + 120) = 70.

Sharmila said: (Jan 3, 2017)  
168 ohms and 41.67v are correct.

Balram Jadhav said: (Jan 25, 2017)  
By using vtg division rule (Vth) = Vs * R3/(R1 + R2 + R3).
and Rth = R1 ll (R2 + R3).

Padam Limbu said: (Mar 5, 2017)  
41.66 v and 70 Ohm is correct.

Eee said: (Apr 11, 2017)  
@ALL.

For the kind information, R3 is opened while calculating Rth. So, actual Rth is 100+68. This is what the Venin's theorem states.

Muzaffar said: (May 3, 2017)  
I = 100/288 = 0.347A.

Rth = 120/(100+68) = 70.

Vth= 0.347 * 120 = 41.6 v.

Mvs said: (Jul 6, 2017)  
Yes, correct @Eee.

When calculating the Venin voltage is equal to open circuit voltage.

Siddhartha said: (Sep 5, 2017)  
What if there is no resistance between A and B terminals?

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