Electrical Engineering Test

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Electrical Engineering Test - 5

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Weekly Quiz Competition

Question 1
2 / -0.66

Determine the constant ‘c’ such that the vector will be solenoidal.

A
c = -1

B
c = -2

C
c = 2

D
c = 1

Solution
Question 2
2 / -0.66

In the circuit shown below 18 V Zener diode has zero Zener resistance and a knee current of 2 mA. The minimum value of R so that voltage across it does not fall below 18 V is:

A
1000 Ω

B
500 Ω

C
9000 Ω

D
2000 Ω
Solution
Concept:

Zener diode as voltage regulator:
- Zener diodes are used in circuits to maintain a fixed voltage across a load.
- It breaks down at a specific voltage when it is reverse biased. This means that a Zener diode will stop a reverse current from flowing through it until the reverse voltage applied across it reaches a fixed value known as the breakdown voltage (V_z).
- It maintains the voltage at its breakdown voltage as long as the supply voltage is above this value.
Zener Knee Current:

The reverse current flows through the Zener diode at the break-down voltage.
Question 3
2 / -0.66

A

B

C

D

Solution

Concept:

According to Mason’s gain formula, the transfer function is given by

Where, n = no of forward paths

M_k = k^th forward path gain

Δk = 1 - Sum of the loop that exists after removal of the k^th forward path + sum of the gain product of two non-touching loops

Δ = 1 – (sum of the loop gains) + (sum of the gain product of two non-touching loops) – (sum of the gain product of three non-touching loops)

Limitations of Mason gain formula

1.) Loop of unity gain value at the output node is invalid, hence neglect it while calculating.

2.) Loop of any gain value at the input node is invalid, hence neglect it while calculating.

Calculation

The transfer function is the ratio of the output node to the input node.

In the transfer function y₇/y₂, y₇ is the output node and y₂ is the input node.

At input node y2 , there are two loops, -G₁H₁ and -G₁G₂G₃H₃ which have to be neglected as per rule 2 of the limitations of the mason gain formula.

The forward path from y₂ to y₇ are:
Question 4
2 / -0.66

Which of the following is NOT one of the representations of discrete-time signals?

A
Sequence representation

B
Graphical representation

C
Analytical representation

D
Tabular representation

Solution

Discrete-time signals are often obtained by sampling continuous-time signals.

There are three ways to represent discrete time signals.

1) Functional Representation.

Example:
Question 5
2 / -0.66

Which of the following statements concerning the LTI system is correct?

1. If the impulse response of an LTI system is periodic and non-zero, then the system is unstable.

2. the inverse of a causal LTI system is always causal.

3. the cascade connection of a non-causal LTI system with a causal one necessarily produces a non-causal system.

A
1 only

B
1 and 2 only

C
2 and 3 only

D
1 and 3 only

Solution

So the cascade connection of a non-causal LIT system with a causal one producing causal system.

Hence, statement 3 is false.
Question 6
2 / -0.66

In a three-phase induction motor, the ratio of starting current to full load current is 12.56 and the ratio of starting torque to full load torque is 1.6. Percentage slip at full load is:

A
0.01%

B
12.64%

C
1%

D
None of these
Solution
Concept:

Methods of Starting 3-Phase Induction Motors:
- Starting current of the induction motor is as high as 5 to 8 times the normal full load current.
- Therefore different starting induction motor, methods are employed to reduce the high starting currents of the induction motor.
- The method to be employed in starting a given induction motor depends upon the size of the motor and the type of the motor.
The common methods used to start induction motors are:
- Direct online starting
- Variable reactor/ resistor starters
- Auto-transformer starters
- Star delta starters
- Rotor Resistance starters
Direct online starting:
- In this method of starting, the motor is started connecting directly to a 3-phase supply.
- This method of starting is suitable for relatively small (up to 7.5 kW) machines.
- Induction motors, when direct switched take five to seven-time their full load current and develops 1.5 to 2.5 times full load torque
Question 7
2 / -0.66

The forward transfer function of a unity feedback system is The system will be

A
stable

B
unstable

C
marginally stable

D
more information is required

Solution

Question 8

2 / -0.66

For the measurement of low resistances following methods are used:

1. Loss of Charge Method

2. Potentiometer Method

3. Substitution Method

4. Kelvin Bridge

Which of the following is/are correct?

1 and 2

2 and 3

3 and 4

2 and 4

Solution

The Measurement of Resistance according to classification is shown below:

	Low Resistance	Medium Resistance	High Resistance
Value	R ≤ 1 Ω	1 to 100 kΩ	R > 100 kΩ
Example	Ammeter internal resistance, Electrical machine winding resistance, Earthing resistance, Diode FB resistance, etc	DC Machine shunt winding resistance, heater coil resistance, Human body under normal condition resistance, etc	Cable insulation resistance, winding insulation resistance, Diode RB resistance, etc
Method of Measurement	1. Potentiometer 2. Kelvin Bridge	1. VA Method 2. Substitution rule 3. Wheatstone Bridge 4. Ohm-meter	1. Loss of charge Method 2. Megger 3. Mega-ohm bridge 4. Direct deflection

Question 9
2 / -0.66

The single-phase half-bridge inverter as shown in the figure here has a resistive load with output power of 240 W and the DC input voltage of V_S = 48 V. Determine the value of load resistance (R) connected?

A
2.4 Ω

B
10 Ω

C
20.6 Ω

D
6.4 Ω

Solution
Question 10
2 / -0.66

For the circuit shown below the transistor α = 0.992, the value of voltage V_BCis

A
8.51 V

B
4.47 V

C
2.16 V

D
10.23 V

Solution

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Electrical Engineering Test - 5

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Electrical Engineering Test - 5

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Question 1

c = -1

c = -2

c = 2

c = 1

Solution

Question 2

1000 Ω

500 Ω

9000 Ω

2000 Ω

Solution

Question 3

Solution

Question 4

Sequence representation

Graphical representation

Analytical representation

Tabular representation

Solution

Question 5

1 only

1 and 2 only

2 and 3 only

1 and 3 only

Solution

Question 6

0.01%

12.64%

1%

None of these

Solution

Question 7

stable

unstable

marginally stable

more information is required

Solution

Question 8

1 and 2

2 and 3

3 and 4

2 and 4

Solution

Question 9

2.4 Ω

10 Ω

20.6 Ω

6.4 Ω

Solution

Question 10

8.51 V

4.47 V

2.16 V

10.23 V

Solution

User

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