Question

In the following circuit, the value of open circuit voltage and the Thevenin resistance between terminals a and b are ___________

(a) VOC = 100 V, RTH = 1800 Ω

(b) VOC = 0 V, RTH = 270 Ω

(c) VOC = 100 V, RTH = 90 Ω

(d) VOC = 0 V, RTH = 90 Ω

I have been asked this question in quiz.

This key question is from Thevenin Theorem Involving Dependent and Independent Sources topic in division Useful Theorems in Circuit Analysis of Network Theory

Answer 1

The correct choice is (d) VOC = 0 V, RTH = 90 Ω

To elaborate: By writing loop equations for the circuit, we get,

VS = VX, IS = IX

VS = 600(I1 – I2) + 300(I1 – I2) + 900 I1

= (600+300+900) I1 – 600I2 – 300I3

= 1800I1 – 600I2 – 300I3

I1 = IS, I2 = 0.3 VS

I3 = 3IS + 0.2VS

VS = 1800IS – 600(0.01VS) – 300(3IS + 0.01VS)

= 1800IS – 6VS – 900IS – 3VS

10VS = 900IS

For Thevenin equivalent, VS = RTH IS + VOC

So, Thevenin voltage VOC = 0

Resistance RTH = 90Ω.