MCQs On Electrical Network Theorem

28
MARCH, 2018

1) An active element in a circuit is one which _____________

2. Supplies energy
3. Both receives and supplies energy
4. None of the above
EXPLANATION
An active component is an electronic component which supplies energy to a circuit.

2) A passive element in a circuit is one which ___________

2. Supplies energy
3. Both receives and supplies energy
4. None of the above
EXPLANATION
A passive element is an electrical component that does not generate power, but instead dissipates, stores, and/or releases it.

3) A linear circuit is one whose parameter _________

1. Changes with change in current
2. Changes with change in voltage
3. Changes with both voltage and current
4. Do not changes with voltage and current
EXPLANATION
A linear circuit is an electric circuit in which circuit parameters (Resistance, inductance, capacitance, waveform, frequency etc) are constant. In other words, a circuit whose parameters are not changed with respect to Current and Voltage is called Linear Circuit.

4) The superposition theorem is used when the circuit contains ____________

1. A single voltage sources
2. A number of voltage sources
3. Only passive elements
4. None of the above
EXPLANATION
The superposition theorem for electrical circuits states that for a linear system the response (voltage or current) in any branch of a bilateral linear circuit having more than one independent source equals the algebraic sum of the responses caused by each independent source acting alone.

5) Norton theorem is ______________ thevenin’s theorem.

1. The same as
2. Converse of
3. Cannot say
4. None of the above
EXPLANATION
Norton’s Thereom is identical to Thevenin’s Theorem except that the equivalent circuit is an independent current source in parallel with an impedance (resistor). Therefore, the Norton equivalent circuit is a source transformation of the Thevenin equivalent circuit.

6) In the analysis of a vacuum tube circuit,we generally use _________ theorem

1. Superposition
2. Thevinin
3. Norton
4. Reciprocity
EXPLANATION
No answer description required for this question.

7) Norton theorem is ________ form of an equivalent circuit.

1. Both current and voltage
2. Current
3. Voltage
4. None of the above
EXPLANATION
Norton’s Theorem is a way to reduce a network to an equivalent circuit composed of a single current source and parallel resistance.

8) In the analysis of transistor theorem, we usually uses _________ theorem.

1. Norton
2. Thevinin
3. Reciprocity
4. Superposition
EXPLANATION
Norton’s theorem is usually used in the analysis of transistor circuit.

9) For transfer of maximum power, the relation between load resistance R and internal resistance r of the voltage source is

1. R = 2r
2. R = 1.5r
3. R = r
4. R = 0.5r
EXPLANATION
The maximum power transfer theorem states that in a linear , bilateral DC network , maximum power is delivered to the load when the load resistance is equal to the internal resistance of a source.

10) Under the condition of maximum power transfer, the efficiency is

1. 100%
2. 75%
3. 50%
4. 25%
EXPLANATION
The efficiency is only 50% when maximum power transfer is achieved.

11) The open circuited voltage at the transfer of load R is 30 V. Under the condition of maximum load power transfer, the load voltage will be _________

1. 30 V
2. 15 V
3. 10 V
4. 5 V
EXPLANATION
Load voltage under maximum power transfer is
= IR
= ( V/(R+r) )×R
= V/2R ×R
= V/2
= 30/2
= 15 V (At max power transfer R=r)

12) The output resistance of a voltage source is 4 Ω. Its internal resistance will be

1. 4 Ω
2. 2 Ω
3. 1 Ω
4. Infinite

EXPLANATION
No answer description required for this question.

13) Star/Delta or Delta/Star technique is applied to ________ network

1. One terminal
2. Two terminal
3. Three terminal
4. None of the above
EXPLANATION
Three branches in an electrical network can be connected in numbers of forms but most common among them is either star or delta form.

14) The resistor value in delta network that is equivalent to a wye containing three 120 Ω resistors is

1. 360 Ω
2. 240 Ω
3. 180 Ω
4. 120 Ω
EXPLANATION
Apply delta to star network conversion formula’s.

15) The resistor values in wye network that is equivalent to a delta containing three 12 kΩ resistor is

1. 2 kΩ
2. 4 kΩ
3. 8 kΩ
4. 36 kΩ
EXPLANATION
Apply delta to star network conversion formula’s.

16) A voltage source has a terminal voltage of 28 V when its terminal are open circuited. When a load of 12 Ω is applied across it terminal, the voltage drops to 24 V. Find the internal resistance of source

1. 0.5 Ω
2. 1 Ω
3. 2 Ω
4. 2.5 Ω
EXPLANATION
EMF of the cell = 28 V
Terminal voltage V = 24
Internal resistance of the cell = ? External load resistance = 12 ohm Load current = 2 Internal resistance r = (E- V)/I
(28–24) / 2= 2 ohm.

17) What percentage of the maximum power is delivered to a load if load resistance is 10 times greater than the thevenin resistance of the source to which it is connected ?

1. 25.06 %
2. 33.06 %
3. 35.06 %
4. 40.06 %
EXPLANATION
PL (max) = ETH / (4RTH )
When RL = 10% RTH , VL = 10RTH / (RTH + 10RTH ) × ETH = (10/11 )ETH PL = (VL2 / RL ) = (10ETH / 11) / 10RTH = (10E2TH / 121RTH )
PL / PL (max) = (10E2TH / 121RTH ) + (E2TH / 4RTH ) = 40/121 = (40/121 )×100

18) Mesh current analysis is based on

1. Kirchhoff’s current law
2. Kirchhoff’s voltage law
3. Maxwell’s law
4. None of the above
EXPLANATION
Mesh analysis is an application of Kirchhoff’s voltage law around the meshes in thee circuit.

19) Nodal analysis is based on

1. Kirchhoff’s current law
2. Kirchhoff’s voltage law
3. Maxwell’s law
4. None of the above
EXPLANATION
Nodal analysis is the application of Kirchhoff’s current law at the non reference nodes.

20) The current through a branch in a linear circuit is 2 A when the input source voltage is 10 V. If the reduced to 1 V and the polarity is reversed, the current through the branch is

1. -0.2 A
2. 0.2 A
3. 2 A
4. -2 A
EXPLANATION
A linear circuit is one whose output is directly proportional to the input. In this case, when voltage is reduced to 1 V, the current is also reduced 10 times i.e. it becomes 0.2 A. As the polarity is reversed, the answer is -0.2 A.

21) The superposition theorem applies to

1. Current / Voltage calculations
2. Power calculations
3. Current and power calculations
4. Voltage and power calculations
EXPLANATION
Since, superposition theorem is based on linearity. it is not applicable to the effect on power (IR) due to each source. Where power is a nonlinear mathematical operation. Therefore, it is applicable to current/voltage calculations.

22) A load is connected to a circuit. At the terminals to which the load is connected, RTH = 10 Ω and VTH  = 40 V. The maximum power supplied to the load is

1. 160 W
2. 80 W
3. 40 W
4. 1 W
EXPLANATION
Under maximum power transfer, RL = RTH and voltage across RL = VTH / 2P(max) = (VTH / 2 )2 / RTH= (40/2)2 / 10= 40 W

23) When a network is loaded by a resistance equal in value to its Norton resistance, the Norton current is IN . The current through the load will be

1. I/ 4
2. 2IN
3. I/ 2
4. None of the above
EXPLANATION
Under maximum power transfer RL = RN Therefore, the Norton current will divide equally between RL and RN so that current through RN is IN/2

24) A 120 V source has a series internal resistance of 1 Ω. The maximum power that can be delivered to a load is

1. 900 W
2. 1800 W
3. 2700 W
4. 3600 W
EXPLANATION
Here, ETTH = 120 V and RTH = 1 Ω
For maximum power in the load, RL = RTH = 1 Ω.
Therefore, voltage across R = ETH /2 = 120/2 = 60 V
P(max)= (60)2/1 = 3600 W

25) A 5 A source has a shunt internal resistance of 100 Ω. The maximum power that can be delivered to a load is

1. 1250 W
2. 625 W
3. 325 W
4. None of the above
EXPLANATION
Here, IN = 5 A and RN = 100 Ω.
For maximum power in the load, RL = RN = 100 Ω.
Therefore, current through load = IN /2 =5/2 = 2.5 A
P(max) = (2.5)2 × RL = (2.5)2 × 100= 625 W
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