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

 

• The circuit is sometimes called a voltage-to-frequency converter because the output frequency can be changed by changing the input voltage.
• Pin 5 terminal is voltage control terminal and its function is to control the threshold and trigger levels.
• Normally, the control voltage is ++2/3V_CC because of the internal voltage divider. However, an external voltage can be applied to this terminal directly or through a pot.
• The voltage across the timing capacitor is depicted in figure, which varies between +Vcontrol and ½ Vcontrol.
• If control voltage is increased, the capacitor takes a longer to charge and discharge; the frequency, therefore, decreases.
• Thus the fre­quency can be changed by changing the control volt­age. Incidentally, the control voltage may be made available through a pot, or it may be output of a transistor circuit, op-amp, or some other device. 

Important Point

• A Monostable multivibrator has a stable state and a quasi-stable state. This has a trigger input to one transistor. So, one transistor changes its state automatically, while the other one needs a trigger input to change its state.
• A Bistable multivibrator has both the two states stable. It requires two trigger pulses to be applied to change the states. Until the trigger input is given, this multivibrator cannot change its state.

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

Concept:

The DC value or the average value of a waveform f(t) is given by the Area under the curve for one complete time period; i.e.,

RMS value 'or' the effective value of an alternating quantity is calculated as:

Calculation:

Average value,

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.

Concept:

Armature Reaction: The effect of Armature (stator) flux on the flux produced by the rotor field poles is called Armature Reaction.

When the current flows through the armature winding of the alternator, a flux is produced by the resulting MMF.

This armature flux reacts with the main pole flux, causing the resultant flux to become either less than or more than the original main field flux.

Explanation:

• Armature reaction of the alternator at zero pf lagging will be purely demagnetizing because at zero pf lagging and will be opposite to each other.

Zero pf lagging → purely demagnetizing

• Armature reaction of the alternator at zero pf leading will be purely magnetizing because at zero pf leading and will be in the same direction to each other.

Zero pf leading → purely magnetizing

• The generator supplies a leading load (as leading load takes the leading VAR) and in return gives lagging VAR (magnetic energy) to the generator.

In case of purely resistive load, the armature reaction is cross magnetizing only.

So, Armature reactance in a synchronous generator at rated voltage and zero power factor leading is only magnetizing.

Important Points

• The armature reaction flux is constant in magnitude and rotates at synchronous speed.
• The armature reaction is cross-magnetizing when the generator supplies a load at unity power factor.
• When the generator supplies a load, at lagging power, the armature reaction is partly demagnetizing and partly cross-magnetizing.​

As shown in the above figure in a power MOSFET, pinch-off occurs when V_DS = V_GS - V_T

Where, V_DS = Drain to source voltage

​V_GS = Gate to source voltage

V_T = Threshold voltage

• In power MOSFET when V_DS < />_GS - V_T, then power MOSFET works in the triode region.
• In power MOSFET when V_DS > V_GS - V_T, then power MOSFET works in the saturation region.

Concept of Feedback System:

• A Feedback System is one in which the output signal is sampled and then fed back to the input to form an error signal that drives the system, and depending on the type of feedback used, the feedback signal which is mixed with the systems input signal, can be either a voltage or a current.
• Feedback will always change the performance of a system and feedback arrangements can be either positive (regenerative) or negative (degenerative) type feedback systems.
• If the feedback loop around the system produces a loop-gain that is negative, the feedback is said to be negative or degenerative with the main effect of the negative feedback is in reducing the system’s gain.
• If however, the gain around the loop is positive, the system is said to have positive feedback or regenerative feedback. The effect of positive feedback is to increase the gain which can cause a system to become unstable and oscillate especially if GH = -1.

Positive feedback:

• In an open-loop system, we do not have any feedback path but in a closed-loop system, we have a feedback path.
• The transfer function of the closed-loop transfer function, with positive feedback, is given by
• The overall gain of the transfer function increases with positive feedback.

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:

Virtual ground -

The concept of the virtual ground is stated as if anyone of the i/p terminals is grounded physically the other i/p terminal will also be at ground potential even though, it is not grounded physically.

• One key feature of an Op-Amp is the differential input, and when put together in a circuit, this can form a virtual ground.
• The virtual ground concept is helpful for the analysis of Op Amps. This concept makes Op-Amp circuit analysis much easier.

Calculation:

By voltage division,

By virtual grand concept, V_a = V_b = V_in

By applying KCL at V_a,

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

The illumination (E) of a surface depends upon the following factors.

• E is directly proportional to the luminous intensity (I) of the source or candle power of the source. i.e. E ∝ I
• Inverse square law: The illumination of a surface is inversely proportional to the square of the distance of the surface from the source, in other words, E ∝ 1/r²
• Lambert’s cosine law: According to this law, E is directly proportional to the cosine of the angle made by the normal to the illuminated surface with the direction of the incident flux
• It is least dependent on ambient temperature

Conversion:

Hexadecimal number to decimal number

(C3B1)16 = (C × 16³) + (3 × 16²) + (B × 16) + (1 × 160)

(C3B1)16 = (12 × 163) + (3 × 162) + (11 × 16) + (1 × 160)

(C3B1)16 = (50097)10

Binary to Hexadecimal conversion table:

Magnetic Fringing:

• One of the properties of the magnetic lines of force states that there is a force of repulsion between the lines of forces which are parallel to each other and are in the same direction
• This repulsive force will cause the magnetic flux to spread out or bulge out at the edges of the air gap as shown in the figure
• The tendency of the magnetic flux to spread out at the edges of the air gap is called Magnetic Fringing

Effects of magnetic fringing:

• Due to the spreading of flux at the edges of the air gap the effective cross-sectional area of the air gap is increased.
• Due to an increased cross-sectional area, the flux density (B) in the air gap is reduced.

Leakage flux and magnetic fringing are an undesirable phenomenon. They can be reduced by selecting high-quality magnetic material and making the air gap as narrow as possible.

Due to the spreading of flux at the edges of the air gap (due to magnetic fringing) the effective cross-sectional area of the air gap increases.

Therefore, Bc > Bg

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:

2’s complement representation:

1) For positive numbers, the 2's complement representation of a number is simply the binary equivalent of the number.

2) For negative numbers, the 2's complement representation is obtained by taking the 2's complement of the binary equivalent of the decimal number.

Analysis:

20 can be represented in binary number system as given below.

20 = 010100

1’s complement = 101011

2’s complement = 1’s complement of the given number + 1

2’s complement = 101011 + 000001 = 101100

Tips and Tricks:

Steps to writing 2’s complement to any binary number:

• Start from right to left and search for the first ‘1’
• Write down the bits until that first ‘1’ as it is.
• Write down the remaining left bits with their respective complement.

Given number is: 010100

2’s complement representation: 101100

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

Finding magnitude and phase:

Given

Va = Vm sin ωt

Vb = Vm sin (ωt + 120°)

Vc = Vm sin (ωt + 240°)

Or Vm sin (ωt - 120°)

Vm = 1

Vbc = Vb - Vc = sin (ωt + 120°) - sin (ωt + 240°)

= √3 × sin (ωt + 90°)

Magnitude = √3

Phase = + 90°

Additional Information

An important point related to the 3 phase system:

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 .

Tirade is a speech of criticism or denunciation, hence adoration is an antonym

As per the meanings given below, the correct idiom will be ‘playing devil’s advocate’.
Take a rain check: postpone a plan.
Rain on someone’s parade: to spoil a moment.
Play devil’s advocate: to argue, just for the sake of it.
Play by the ear: to improvise.
Correct Sentence:
He was not agreeing to back off, as if he was playing devil’s advocate.
Hence, the correct answer is option C. 

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 .

Which service provides 3D view of earth?
The service that provides a 3D view of the Earth is Google Earth.
Google Earth:
- Google Earth is a virtual globe, map, and geographical information program that allows users to explore and navigate the Earth in 3D.
- It provides a detailed view of the Earth's surface, including landscapes, buildings, and landmarks.
- Users can zoom in and out, rotate the view, and navigate to different locations around the world.
- It offers features such as Street View, which allows users to view and navigate through street-level imagery.
- Google Earth also provides historical imagery, allowing users to see how a location has changed over time.
- It is available as a desktop application and also as a web-based version called Google Earth Web.
Wikipedia:
- Wikipedia is an online encyclopedia that provides information on various topics, including Earth-related information.
- While Wikipedia may include images and maps of the Earth, it does not offer a 3D view of the Earth like Google Earth.
Skype:
- Skype is a telecommunications application that provides video chat and voice call services.
- It does not provide a 3D view of the Earth.
None of these:
- This option is incorrect as Google Earth does provide a 3D view of the Earth.
In conclusion, the service that provides a 3D view of the Earth is Google Earth.

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.

Explanation:
The application of the internet refers to the various ways in which the internet is used in our daily lives. The internet has revolutionized the way we communicate, conduct business, and access information. However, there are certain activities that are not considered as applications of the internet.
Here, the option "D: Sleeping" is not an application of the internet. Sleeping is a biological process and does not involve the use of the internet. The internet cannot be directly used for sleeping purposes.
Applications of the Internet:
A: Communication
- The internet allows people to communicate with each other through various means such as email, instant messaging, video calls, and social media platforms.
- It enables people to connect with others globally, facilitating communication in real-time.
B: Banking
- The internet is widely used for online banking services, allowing individuals to access their bank accounts, make transactions, and manage their finances online.
- It provides convenience and accessibility to banking services from anywhere at any time.
C: Shopping
- Online shopping has become increasingly popular with the advent of the internet.
- It allows consumers to browse and purchase products from various online retailers, making shopping more convenient and accessible.
In summary:
The internet has numerous applications, including communication, banking, and shopping. However, sleeping is not an application of the internet as it does not involve the use of online services or activities.

Daughter of grandmother = Aunt
Aunt’s only brother = Father

All these are part of a vehicle.