BEL Trainee Engineer Electrical Mock Test - 8 - Electrical Engineering (EE) MCQ

SCRs are constructed from silicon and are most commonly used for converting AC current to DC current (rectification), hence the name Silicon controlled rectifier.

They are also used in other applications such as regulation of power, inversion, etc.

The SCRs have an ability to handle high value of current and Voltage hence they are used in most of the industrial applications.

SCR has three terminals namely Anode (A), Cathode (K) and gate (G), and it can be turned ON or OFF by controlling the biasing conditions or the gate input.

SCR can operate in three different modes

• Forward Blocking mode
• Forward Conduction mode
• Reverse Blocking mode

Among all of the options, high rate of rise of voltage does not cause permanent damage to an SCR

The damper winding in synchronous motor performs two functions:

• Prevents hunting (damped out oscillations)
• Provides starting torque (made self-starting)

Under normal running conditions, damper winding does not carry any current.

Hunting is the phenomenon that occurs in synchronous motors due to varying load or supply frequency.

Causes of hunting

• Periodic variation of load
• Sudden changes in load
• Faults occurring in the system when supplied by the generator
• Sudden change in the field current
• Cyclic variations of the load torque

Effects of hunting

• It can lead to loss of synchronism
• It can cause variations of the supply voltage producing undesirable lamp flicker
• The possibility of resonance condition increases. If the frequency of the torque component becomes equal to that of the transient oscillations of the synchronous machine, resonance may take place
• Large mechanical stresses may develop in the rotor shaft
• The machine losses increases and the temperature of the machine rises

Concept:

A system is said to be causal if the system is dependent on the present or past inputs only but not on the future input.

A system is time-invariant if a time shift in the input signal results in an identical time shift in the output signal.

y(n) = x(n) and y(n-k) = x (n – k)

A system is said to be linear if it follows both superposition and homogeneity.

A system is said to be stable if it gives bounded input for bounded input.

Application:

y[n] = x[n – 1]

y₁[n] = x₁[n – 1]

y₂[n] = x₂[n – 1]

y₃[n] = x₁[n – 1] + x₂[n – 1]

= y₁[n] + y₂[n]

The given system satisfies superposition principle.

y₁[n] = ax₁[n – 1] = ay[n]

The given system satisfied homogeneity principle.

As the system is satisfying both superposition and homogeneity, it is a linear system.

For the given system, the present output depends on the value of inputs only. Therefore, the system is causal.

As the output of the system is depends on the past inputs, the system is dynamic i.e. not memoryless.

The main objective of the governor system in power systems for all types of turbines is to control the frequency. A governor protects the prime mover from over speed and keeps the prime mover speed at or near the desired revolutions per minute. When a prime mover drives an alternator supplying electrical power at a given frequency, a governor must be used to hold the prime mover at a speed that will yield this frequency.

The correct answer is 6.

Concept:

The Fourier series representation of a periodic signal with a fundamental period T and fundamental frequency ω0 = 2π/T is given by:

Where X[k] is the Fourier series co-efficient,

Analysis:

The value of k going up to infinity and distance between each Fourier coefficient is its own fundamental frequency.

Highest frequency allowed by filter = 50 rad/sec

Now highest value of k = = = 6.25

so k > 6;

X[k] is zero

Hence, the maximum value of k for which X(k) is non-zero = 6

Parseval's Theorem:

For continuous-time, periodic signal, the energy is given by:

Where ak is the Fourier series coefficient of x(t), and T is the period of the signal.

For average power in one period of the periodic signal x(t), we write:

∴ is the average power in the kth harmonic of x(t).

∴ Parseval's relation states that the total average power in a periodic signal equals the sum of the average powers in all of its harmonic components.

Concept:

The Fourier Transform of a continuous-time signal x(t) is given as:

Analysis:

Given:

x(t) = e^j10t defined from t = -1 to 1.

Concept:

• In 8085 Instruction, XRA is a mnemonic that stands for “eXclusive OR Accumulator” and “R” stands for any of the following registers, or memory location M pointed by HL pair.
• R = A, B, C, D, E, H, L, or M
• This instruction is used to Ex-OR contents of R with the Accumulator. The result of the Ex-OR operation will be stored in the Accumulator.
• As R can have any of the eight values, there are eight opcodes for this type of instruction. It occupies only 1-Byte in memory.

e.g. MVI A, 05 H

XRA A

(0000 0101) EXOR (0000 0101) = (0000 0000)

Application:

The accumulator contains 00 H after the execution of an instruction

And Zero flag is set

Norton’s theorem is applied to the DC circuits, it will result in a current source with resistance in parallel.

Thevenin’s theorem is applied to the DC circuits, it will result in a voltage source with a resistance in series.

Lead compensator:

Transfer function:

If it is in the form of , then a > 1

If it is in the form of , then a < />

Maximum phase lead frequency:

Maximum phase lead:

ϕ_m is positive

Pole zero plot:

The zero is nearer to the origin.

Filter: It is a high pass filter (HPF)

Effect on the system:

• Rise time and settling time decreases and Bandwidth increases
• The transient response becomes faster
• The steady-state response is not affected
• Improves the stability

Lag compensator:

Transfer function:

If it is in the form of , then a < />

If it is in the form of , then a > b

Maximum phase lag frequency:

Maximum phase lag:

ϕ_m is negative

Pole zero plot:

The pole is nearer to the origin.

Filter: It is a low pass filter (LPF)

Effect on the system:

• Rise time and settling time increases and Bandwidth decreases
• The transient response becomes slower
• The steady-state response is improved
• Stability decreases

The type of system is the number of poles present at the origin in the open-loop transfer function.

In Bode plot,

• The initial slope for each pole at origin is -20 dB/decade or -6 dB/octave.
• The initial slope for each zero at origin is +20 dB/decade or +6 dB/octave.
• The initial slope is zero if there are no poles or zeros at the origin.

The initial shape of the Bode plot gives an indication of the type of the system.

Concept:

The Series R-L circuit with DC source is shown below as.

Formula:

The voltage across the resistor is

The voltage across the Inductor is

The formula for alternating current passes through the R-L circuit is

Calculation:

Concept:

Differentiation in s domain:

Consequently, if

Then

Application:

X(s) = 3s² + 2s + 1

X₁(s) = 6s + 2

By applying inverse Laplace transform, we get

⇒ x₁(t) = -tx(t)

Concept:

The condition for optimum operation and economic dispatch is

Where,

is incremental fuel costs in Rs/MWh for a power plant.

The above equation shows that the criterion for a most economical division of load between a plants is that all the unit is must operate at the same incremental fuel cost.

Calculation:

Given, Incremental fuel costs

For optimum operation

⇒ 0.4P₁ + 400 = 0.48P₂ + 320

⇒ -0.4P₁ + 0.48P₂ = 80

Total load shared by the two generating plant is

P₁ + P₂ = 900

On solving above equations, we get

P₁ = 400 MW, P₂ = 500 MW

Concept:

Impedance of a coil

Z = R + jX_L

R = resistance of the coil

X_L = ωL = 2π fL = Reactance of coil

Calculation:

1) When coil Connected to 220 V DC supply

Current in the coil = 2.2 A

X_L = 2π fL = 0 ohm { for DC supply f = 0 }

2) When coil connected to 220 V, 50 Hz AC supply

Current in the coil = 1 A

Z = R + jX_L

Z² = R² + X_L² = (220)² = (100)² + (X_L)²

X_L = 195.95 ohm = 2π fL

L = 0.624 H

Use structure “subject + auxiliary + past participle + by + object”
As per the given above sentence is given in Passive Voice.
The wounded woman was being helped by some people.
Therefore ,required answer will be option B .

We can say that ,
The above given sentence is given in Passive Voice :-
Use structure “subject + auxiliary + past participle + by + object”
The beggar was laughed at by the boy.
Thus , option B will be required answer .

Long term scheduling
- Determines when new processes are admitted to the system
- Also known as admission scheduling or job scheduling
- Determines which processes should be brought into the system from the job pool or job queue
- Decides when a new process can be created and executed in the system
- Mainly focuses on managing the resources required by the processes and ensuring that the system does not become overloaded
Medium term scheduling
- Involves swapping processes between main memory and secondary memory (e.g., hard disk)
- Decides which processes should be swapped out of main memory and which should be brought back in
- It is responsible for managing the degree of multiprogramming or the number of processes in the ready state that are kept in main memory
Short term scheduling
- Also known as CPU scheduling
- Determines which process should be executed next by the CPU
- Determines the order in which ready processes are allocated the CPU for execution
- Focuses on improving the performance of the system by minimizing the waiting time and maximizing the CPU utilization
- Examples of short-term scheduling algorithms include First-Come, First-Served (FCFS), Round Robin, and Shortest Job Next (SJN)
None of these
- This option is incorrect as one of the above options is the correct answer

Explanation:
The internet packet data structure consists of several components that are necessary for the successful transmission of data packets between source and destination addresses. These components include:
1. Source address: The IP address of the sender or source device.
2. Destination address: The IP address of the receiver or destination device.
3. Serial number of packets: Each packet is assigned a unique serial number to ensure proper sequencing during transmission.
4. Message bytes: The actual data or message being transmitted in the packet.
5. Control bits for error checking: These bits are used for error detection and correction during transmission.
6. Path identification bits: These bits help to identify the specific path or route that the packet should follow to reach its destination.
Based on the given options, the correct answer is option C, which includes all the mentioned components (i, ii, iii, iv, and v) in the internet packet data structure. Option D includes an additional component (vi) of path identification bits, but it is not mentioned in the provided information. Therefore, the correct answer is option C.

The facilities available on the internet are:
Electronic mail:
- Electronic mail, or email, is a widely used facility on the internet.
- It allows users to send and receive messages electronically.
- Email can be used for communication purposes, both personal and professional.
Remote login:
- Remote login allows users to access another computer or network remotely.
- It enables users to connect to a remote computer and access its resources.
- Remote login is commonly used for remote troubleshooting, accessing files, and managing servers.
File transfer:
- File transfer is another facility available on the internet.
- It allows users to transfer files from one computer to another.
- File transfer can be done using protocols such as FTP (File Transfer Protocol) or through cloud storage services.
Word processing:
- Word processing is a facility that allows users to create, edit, and format documents.
- There are various online word processing tools available on the internet.
- Users can create and collaborate on documents in real-time using these tools.
Answer: Option B: i, ii, iii.

The network topology with bi-directional links between each possible node is called a Mesh topology.
Explanation:
In a Mesh topology, each node in the network is connected to every other node through individual bi-directional links. This means that there is a direct connection between each pair of nodes in the network.
Here are some key points about Mesh topology:
- Full Mesh: In a full mesh topology, each node has a direct connection with every other node in the network. This provides high redundancy and fault tolerance but requires a large number of physical connections.
- Partial Mesh: In a partial mesh topology, only some nodes have direct connections with other nodes. This reduces the number of physical connections required but still provides some redundancy and fault tolerance.
- Advantages: Mesh topology offers several advantages, including:
- High fault tolerance: If one link or node fails, there are alternative paths for communication.
- High scalability: It is easy to add or remove nodes without affecting the rest of the network.
- High security: Each node has its own dedicated connection, making it difficult for unauthorized access.
- High performance: Mesh topology allows for parallel and simultaneous data transmission between nodes.
- Disadvantages: However, there are also some disadvantages to using a Mesh topology:
- High cost: The implementation of numerous physical connections can be expensive.
- Complex management: With a large number of connections, managing and troubleshooting the network can be challenging.
- High redundancy: In a full mesh topology, there may be redundant connections that are not regularly utilized.
In conclusion, a Mesh topology provides a highly interconnected network where each node has a direct link to every other node in the network, allowing for efficient communication and high fault tolerance.

Introduction:
In this question, we are asked to identify the characteristics of a laser printer. We need to choose the correct options from the given choices.
Characteristics of a laser printer:
A laser printer is a type of printer that uses laser technology to produce high-quality prints. Let's analyze each statement given in the question and determine its accuracy:
1. Prints an entire line at a time:
- This statement is true. Laser printers use a process called "electrophotography" or "xerography" to print an entire line at a time. This process involves the use of a laser beam to create an electrostatic image of the entire line on a photosensitive drum.
- Correct
2. Non-impact printer:
- This statement is true. Laser printers are non-impact printers, which means they do not require direct contact between the print head and the paper to create an image. Instead, they use a laser beam to transfer toner onto the paper.
- Correct
3. Allows multiple copies to be taken at a time:
- This statement is false. Laser printers generally do not allow multiple copies to be taken at a time. However, some advanced laser printers may have features like duplex printing or collating, which can produce multiple copies in a single print job.
- Incorrect
4. Prints one character at a time:
- This statement is false. Laser printers do not print one character at a time. As mentioned earlier, they print an entire line at a time using a laser beam and electrostatic imaging.
- Incorrect
Conclusion:
Based on the analysis, we can conclude that the correct characteristics of a laser printer are:
- Prints an entire line at a time
- Non-impact printer
Therefore, the correct answer is (A) i and ii.

To determine the size of a monitor, we measure the screen diagonally, from the top left corner to the bottom right corner. Here's a detailed explanation:
Diagonal Measurement:
- The size of a monitor is typically measured diagonally because it provides an accurate representation of the screen's actual size.
- The diagonal measurement is obtained by measuring the distance from the top left corner of the screen to the bottom right corner in a straight line.
- This measurement helps us understand the physical size of the screen and is commonly used to compare and select monitors.
Other Measurements:
- While diagonal measurement is the standard for determining monitor size, other measurements are also important for specific purposes.
- Vertical measurement refers to the distance from the top to the bottom of the screen, which is essential for understanding the screen's height.
- Horizontal measurement refers to the distance from the left to the right of the screen, which helps in determining the screen's width.
- However, these measurements alone do not provide a comprehensive understanding of the monitor's size.
Conclusion:
In conclusion, the size of a monitor is determined by measuring the screen diagonally, from the top left corner to the bottom right corner. This measurement provides an accurate representation of the screen's size and is commonly used for comparing and selecting monitors.

Shortcut Key to Insert Current Date in a Cell:
To insert the current date in a cell in Microsoft Excel, you can use a shortcut key combination. The correct shortcut key to achieve this is CTRL ;.
Here's a detailed explanation:
1. Open Microsoft Excel and navigate to the desired worksheet.
2. Click on the cell where you want to insert the current date.
3. Press the CTRL key on your keyboard and hold it down.
4. While still holding down the CTRL key, press the ; (semicolon) key.
5. Release both keys.
6. The current date will be inserted into the selected cell.
Note: The inserted date will remain static and will not automatically update to the current date unless you manually refresh it.
Additional Shortcut Keys:
In addition to the shortcut key mentioned above, here are a few other helpful shortcuts in Microsoft Excel:
- CTRL D: This shortcut is used to fill down the contents of the selected cell or cells from the cell above.
- CTRL T: This shortcut is used to create a new table from the selected data range.
- CTRL /: This shortcut is used to start a comment in the active cell.

Remember to use the appropriate shortcut key based on the specific action you want to perform in Microsoft Excel.

An audio output unit
An audio output unit refers to a device that produces sound or audio output. Here are some key points to understand about audio output units:
1. Can speak out small range of digits and specified words:
- Audio output units are capable of producing sound in the form of spoken words and digits.
- They can be programmed to speak out specific words or digits, such as phone numbers, addresses, or other predetermined information.
2. Is not used in information system:
- This statement is incorrect. Audio output units are commonly used in information systems to provide auditory feedback or instructions to users.
- For example, automated phone systems often use audio output units to provide instructions or read out options to callers.
3. Is very expensive and is thus not used:
- This statement is also incorrect. Audio output units come in a wide range of prices, depending on their complexity and capabilities.
- While some high-end audio output units may be expensive, there are also many affordable options available in the market.
4. Is normally used to give only background music:
- This statement is incorrect. While audio output units can be used to play background music, their functionality extends far beyond that.
- They are commonly used in various applications such as multimedia systems, gaming consoles, public announcement systems, and more.
In conclusion, an audio output unit is a versatile device used for producing sound or audio output. It can speak out a small range of digits and specified words, is commonly used in information systems, comes in a wide range of prices, and can be used for various purposes beyond playing background music.

Hence, option B is correct.

As per the given information;

Hence, Rima is in South direction from her starting point.

The answer is B: Eagle.

Explanation:
Kiwi, Emu, and Ostrich:
- These are all flightless birds.
- They belong to a group of birds called ratites, which have flat breastbones without a keel.
- They are generally large, ground-dwelling birds that rely on running for defense and movement.
Eagle:
- Eagles are powerful birds of prey.
- They have strong wings and are capable of flight.
- They belong to the family Accipitridae, which includes hawks, kites, and harriers.
Conclusion: The word that is different from the rest is B: Eagle, because it is a bird of prey capable of flight, while the others are flightless birds.