Thevenin’s Theorem MCQ [Free PDF] – Objective Question Answer for Thevenin’s Theorem Quiz

Electrical MCQ / May 28, 2022

21. A circuit is given in the figure below. The Thevenin equivalent as viewed from terminals x and x’s is ___________

A circuit is given in the figure below. The Thevenin equivalent as viewed from terminals x and x’ is ___________

A. 8 V and 6 Ω
B. 5 V and 6 Ω
C. 5 V and 32 Ω
D. 8 V and 32 Ω

Answer: B

We, Thevenized the left side of xx’ and source transformed the right side of yy’.

A circuit is given in the figure below. The Thevenin equivalent as viewed from terminals x and x’ is ___________

Vxx’  = Vth = \(\displaystyle\frac{\frac{4}{8} + \frac{8}{24}}{\frac{1}{8} + \frac{1}{24}}\) = 5V

 

∴ Rth  = 8 || (16 + 8)

= (8×24)/(8 + 24) = 6 Ω.

 

22. For the circuit given in the figure below, the Thevenin equivalent as viewed from terminals y and y’ is _________

A circuit is given in the figure below. The Thevenin equivalent as viewed from terminals x and x’ is ___________

A. 8 V and 32 Ω
B. 4 V and 32 Ω
C. 5 V and 6 Ω
D. 7 V and 6 Ω

Answer: D

We, Thevenized the left side of xx’, and the source transformed the right side of yy’.

A circuit is given in the figure below. The Thevenin equivalent as viewed from terminals x and x’ is ___________

Thevenin equivalent as seen from terminal yy’ is

Vxx’ = Vth = \(\displaystyle\frac{\frac{4}{8} + \frac{8}{24}}{\frac{1}{8} + \frac{1}{24}}\) = 5V

(0.167 + 1)/(0.04167 + 0.125) = 7 V
∴ Rth  = (8 + 16) || 8

= (24×8}/(24 + 8) = 6 Ω.

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23. In the following circuit, when R = 0 Ω, the current IR equals to 10 A. The value of R, for which maximum power is absorbed by it is ___________

In the following circuit, when R = 0 Ω, the current IR equals to 10 A. The value of R, for which maximum power is absorbed by it is

A. 4 Ω
B. 3 Ω
C. 2 Ω
D. 1 Ω

Answer: C

The Thevenin equivalent of the circuit is as shown below.

In the following circuit, when R = 0 Ω, the current IR equals to 10 A. The value of R, for which maximum power is absorbed by it is

Therefore from the figure, we can infer that Rth  = 2 Ω

 

24. In the following circuit, when R = 0 Ω, the current IR equals to 10 A. The maximum power will be?

In the following circuit, when R = 0 Ω, the current IR equals to 10 A. The value of R, for which maximum power is absorbed by it is

A. 50 W
B. 100 W
C. 200 W
D. 400 W

Answer: A

The Thevenin equivalent of the circuit is as shown below.

I = 10 A, Rth  = 2 Ω

∴ Pmax = (10/2)2 × 2

= 5×5×2 = 50 W.

 

25. For the circuit given below, the Thevenin resistance across the terminals A and B is ________

For the circuit given below, the Thevenin resistance across the terminals A and B is ________

A. 5 Ω
B. 7 kΩ
C. 1.5 kΩ
D. 1.1 kΩ

Answer: B

Let VAB  = 1 V

5 VAB  = 5

Or, 1 = 1 × I1 or, I1  = 1

Also, 1 = − 5 + 1(I – I1)

∴ I = 7

Hence, R = 0.2 kΩ.

 

26. For the circuit given below, the Thevenin voltage across the terminals A and B is ____________

For the circuit given below, the Thevenin resistance across the terminals A and B is ________

A. 1.25 V
B. 0.25 V
C. 1 V
D. 0.5 V

Answer: D

Current through 1 Ω = (5/2) – I1

Using source transformation to 5 V sources

VOC  = 1 × I1

VOC  = − 5 VOC + (5/2) – I1) × 1

Eliminating I1, we get, VOC  = 0.5 V.

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27. In the following circuit, the value of open-circuit voltage and the Thevenin resistance between terminals a and b are ________

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

Answer: D

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.

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28. In the circuit given below, it is given that VAB  = 4 V for RL  = 10 kΩ and VAB  = 1 V for RL  = 2kΩ. The values of the Thevenin resistance and voltage for the network N are ____________

In the circuit given below, it is given that VAB = 4 V for RL = 10 kΩ and VAB = 1 V for RL = 2kΩ. The values of the Thevenin resistance and voltage for the network N are ____________

A. 16 kΩ and 30 V
B. 30 kΩ and 16 V
C. 3 kΩ and 6 V
D. 50 kΩ and 30 V

Answer: B

When RL  = 10 kΩ and VAB  = 4 V

Current in the circuit

I = VAB/RL = 4/10 = 0.4 mA

Thevenin voltage is given by

VTH  = I (RTH  + RL)

= 0.4(RTH  + 10)

= 0.4RTH  + 4

Similarly, for RL  = 2 kΩ and VAB  = 1 V

So, I = 1/2 = 0.5 mA

VTH  = 0.5(RTH  + 2)

= 0.5 RTH  + 1

∴ 0.1RTH  = 3

Or, RTH  = 30 kΩ

And VTH  = 12 + 4 = 16 V.

 

29. For the circuit shown in the figure below, the value of the Thevenin resistance is _________

For the circuit shown in figure below, the value of the Thevenin resistance is _________

A. 100 Ω
B. 136.4 Ω
C. 200 Ω
D. 272.8 Ω

Answer: A

IX  = 1 A, VX  = Vtest

Vtest  = 100(1 − 2IX) + 300(1 − 2IX – 0.01VS) + 800

Or, Vtest  = 1200 – 800IX – 3Vtest

Or, 4Vtest  = 1200 – 800 = 400

Or, Vtest  = 100V

∴ RTH = Vtest/1 = 100 Ω.

 

30. For the circuit shown in the figure below, the Thevenin voltage and resistance looking into X − Y are __________

For the circuit shown in the figure below, the Thevenin voltage and resistance looking into X-Y are __________

A. 4/3 V and 2 Ω
B. 4V and 2/3 Ω
C. 4/3 V and 2/3 Ω
D. 4 V and 2 Ω

Answer: D

RTH = Voc/Isc

VTH  = VOC

Applying KCL at node A,

\(\frac{2I − V_{TH}}{1} + 2 = I + \frac{V_{TH}}{2}\)

Or, I = VTH/1

Putting, 2VTH – VTH  + 2 = VTH + VTH/2

Or, VTH  = 4 V.

∴ RTH  = 4/2 = 2Ω.

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31. In the figure given below by using Thevenin’s Theorem find the value of the source voltage is ___________

In the figure given below, the value of the source voltage is ___________

A. 12 V
B. 24 V
C. 30 V
D. 44 V

Answer: C

By applying KCL

\(\frac{V_P − E}{6} + \frac{V_P}{6}\) – 1 = 0

Or

2 VP – E = 6

Where

(\(\frac{ − V_P + E}{6}\)) = 2

∴ E – VP  = 12

Or, VP  = 18 V

∴ E = 30V.

 

32. In the figure given below, the value of Resistance R by the Thevenin Theorem is ___________

In the figure given below, the value of Resistance R by Thevenin Theorem is ___________

A. 10
B. 20
C. 30
D. 40

Answer: B

\(\frac{V_P − 100}{10} + \frac{V_P}{10}\) + 2 = 0

 

Or, 2VP – 100 + 20 = 0

∴ VP  = 80/2 = 40V

∴ R = 20Ω.

 

33. In the figure given below, the Thevenin’s equivalent pair, as seen at the terminals P − Q, is given by __________

In the figure given below, the Thevenin’s equivalent pair, as seen at the terminals P-Q, is given by __________

A. 2 V and 5 Ω
B. 2 V and 7.5 Ω
C. 4 V and 5 Ω
D. 4 V and 7.5 Ω

Answer: A

For finding VTH,

VTH = (4 ×10)/(10 + 10) = 2V

For finding RTH,

RTH  = 10 || 10

= (10×10)/(10 + 10) = 5 Ω.

 

34. The Thevenin equivalent impedance Z between the nodes P and Q in the following circuit is __________

The Thevenin equivalent impedance Z between the nodes P and Q in the following circuit is __________

A. 1
B. 1 + s + 1/s
C. 2 + s + 1/s
D. 3 + s + 1/s

Answer: A

To calculate the Thevenin resistance, all the current sources get open-circuited and voltage sources short-circuited.

(\(\frac{1}{s}\) + 1) || (1 + s) = \(\frac{\left(\frac{1}{s} + 1\right)×(1 + s)}{\left(\frac{1}{s} + 1\right) + (1 + s)}\)

 

= \(\frac{\frac{1}{s} + 1 + 1 + s}{\frac{1}{s} + 1 + 1 + s}\) = 1
So, RTH  = 1.

 

35. While computing the Thevenin equivalent resistance and the Thevenin equivalent voltage, which of the following steps are undertaken?

  1. Both the dependent and independent voltage sources are short-circuited and both the dependent and independent current sources are open-circuited
  2. Both the dependent and independent voltage sources are open-circuited and both the dependent and independent current sources are short-circuited
  3. The dependent voltage source is short-circuited keeping the independent voltage source untouched and the dependent current source is open-circuited keeping the independent current source untouched
  4. The dependent voltage source is open-circuited keeping the independent voltage source untouched and the dependent current source is short-circuited keeping the independent current source untouched
Answer: C

While computing the Thevenin equivalent voltage consisting of both dependent and independent sources, we first find the equivalent voltage called the Thevenin voltage by opening the two terminals.

Then while computing the Thevenin equivalent resistance, we short-circuit the dependent voltage sources keeping the independent voltage sources untouched, and open-circuiting the dependent current sources keeping the independent current sources untouched.

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