BEL Trainee Engineer Electrical Mock Test - 2 - Electrical Engineering (EE) MCQ

Ohm’s law in the case of magnetic circuits can be stated as, the magnetic flux developed in the circuit is directly proportional to magnetomotive force. The relation is similar to Ohm’s law and can be formed by replacing electromotive force (emf) with mmf and electric current (i) with magnetic flux.

Flux = mmf/reluctance.

ϕ = mmf/S

Important Points:

Magnetic circuits are analogous to electric circuits. Some of the quantities are given below.

Concept:

In a chopper, the duty cycle is defined as the ratio of on-time to the time period.

D = T_on/T

T = T_on + T_off­

T_on is the on-time

T_off is the off-time

Calculation:

Given that, chopping frequency (f) = 1 kHz

Time period (T) = 1/1k = 1 ms

On time (T_on) = 0.5 msec

Duty ratio = 0.5/1 = 0.5

Concept:

The discrete-time Fourier transform of a given signal x(n) is given by,

Time-shifting property of FT:

If X(ω) is the Fourier transform of x(n),

then e^-jωkx(ω) is the Fourier transform of x(n – k).

Application:

Let the signal is,

x(n) = u(n)

The Fourier transform of the signal x(n) is,

By applying the property of shifting, the Fourier transform of x(n – k) is

Concept:

Force on a current carrying conductor in a magnetic field

Where, B = magnetic flux density

I = current

L = length of conductor

Calculation:

Given that, I = 2 A, l = 0.5 m, B = 0.05 Wb/m2

Force, F = 0.05 × 2 × 0.5 = 0.05 N

Hysteresis motor:

• A hysteresis motor is a synchronous motor with a uniform air gap and without DC excitation
• The torque in a hysteresis motor is produced due to hysteresis and eddy current induced in the rotor by the action of the rotating flux of the stator windings
• The hysteresis losses are very high. As the hysteresis losses are directly proportional to the area of the hysteresis loop, the hysteresis loop is very large.
• It has high starting torque as it has high rotor hysteresis loss
• It accelerates from rest to full-speed almost instantaneously
• It is not sensitive to fluctuations in supply voltage
• The noise level of the hysteresis motor is very low as compared to the induction motor because it operates at a constant speed and its rotor is smooth
• This type of motor is the smoothest running, quietest single-phase motor and is used for quality sound reproduction equipment like record players, tape recorders, etc.

Q meter is an instrument which is designed to measure the value of quality factor directly and it is useful in measuring the characteristics of coils and capacitors.

Important:

• Q meter works on the principle of series resonance.
• At series resonance, the voltage across capacitor is equal to Q times of applied input voltage. Thus, we can measure the value of Q directly by connecting a voltmeter across capacitor.
• It is used for the measurement of quality factor, inductance, self-capacitance, inductance, bandwidth and capacitance of a coil.

Concept:

Peak to peak amplitude of the signal voltage (V_P-P) = Vertical sensitivity × divisions corresponds to peak to peak amplitude

The maximum voltage or peak voltage is given by,

The average value of the sinusoidal wave,

Calculation:

Vertical sensitivity = 4 V/cm

Divisions correspond to peak to peak amplitude = 8 cm

Peak to peak amplitude of the signal voltage (V_P-P) = 4 × 8 = 32 V

The maximum voltage or peak voltage, V_m = 32/2 = 16 V

The average value of the voltage, 

Relative permittivity:

• Relative permittivity ε_r (also dielectric constant) is a measure of polarization of a material in electric field (the higher the permittivity the greater is polarization of the material).
• Polarization occurs when electric field displaces charge carriers in atoms (electron polarization), molecules (atom polarization), molecule groups (molecular polarization) or crystals (lattice polarization).
• The liquid-impregnated material has higher value of relative permittivity than the cellulose material alone but ideally it should be same as the cellulose material.

A porous solid dielectric has a relative permittivity of 4.

It is to be impregnated by a liquid dielectric whose relative permittivity should ideally be 4.

Concept:

Each zero at origin gives a phase shift of + 90°

For N zeros at origin gives a phase shift of + 90N°

Each pole at origin gives a phase shift of - 90°

For N poles at origin gives a phase shift of - 90N°

Calculation:

The given transfer function = 1/s²

Number of poles at origin = 2

Phase shift = 2 × (- 90°) = - 180°

Additional Information

Minimum phase system: It is a system in which poles and zeros will not lie on the right side of the s-plane.

For a minimum phase system:

Where P & Z are finite no. of poles and zeros of G(s)H(s)

Non-minimum phase system: It is a system in which some of the poles and zeros may lie on the right side of the s-plane.

In particular, zeros lie on the right side of the s-plane.

All pass system: An all-pass network is the network that is the combination of the minimum and non-minimum phase systems and have the unity magnitude for all

frequencies and imparts only a 180-degree phase shift. The pole and zero of an all-pass filter are at the same distance from the origin.

Concept:

X’ = Ax + Bu → (1)

Y = Cx + Du → (2)

Apply Laplace transform, to equation (1)

S x(s) = A x(s) B u(s)

⇒ B u(s) = (SI - A) X(s)

⇒ X(s) = (SI - A)-1 B u(s)

Now apply Laplace transform to equation (2)

Y(s) = C x(s) + D u(s)

⇒ Y(s) = C[(SI - A)-1] B u(s) + D u(s)

Calculation:

From the given state-space representation,

• In a 3-phase converter circuit, during commutation when one SCR in one phase is turned on, turning of an SCR in another phase results is voltage notching.
• During the brief time when the current is transferred from one conducting SCR to another, a short circuit is created.
• The incoming SCR would have started conduction whereas the outgoing SCR will not have stopped conduction completely.
• This causes a phase-phase short circuit (for a very minute duration usually in micro seconds) enough to depress the voltage. This is the fundamental mechanism of voltage notch creation.
• Notch may occur at any point during the AC half cycle as the angle of commutation is not a constant value and keeps changing to meet the requirements of the load.

Concept:

The current in each parallel path = I/A

A is the number of parallel paths

In a wave wound generator, number of parallel paths = 2

In a lap wound generator, number of parallel paths = number of poles

Calculation:

Power (P) = 25 kW

Voltage (V) = 200 V

Total current

Number of parallel paths = 2

The current in each parallel path = 125/2 = 62.5 A

Concept:

Low pass filter:

Circuit diagram of the low-pass filter

This filter passes the low frequency and passes the low frequency.

Substitute s = jω

Gain is maximum when ω equals zero (ω = 0)

Where A_m is the maximum gain

For 3 dB frequency gain A = A_m / √2

⇒ 2 = 1 + (ωRC)²

⇒ ω = 1 / RC

⇒ f = 1 / 2πRC

Calculation:

Given,

Resistance R = 2 kΩ

Frequency f = 7.5 kHz

Required coupling capacitor C = 1 / 2πfR

⇒ C = 1 / 2π × 7.5 × 10³ × 2 × 10³ = 0.01 μF

Therefore, the coupling capacitor required is 0.01 μF (0.01 micro farad)

Concept:

Standard Z transform: 

Differentiation property: 

Application:

The double integral of the unit sample in discrete form is given as

X[n] = n. u[n]

One word substitution is Incorrigible.

Unintelligible: Impossible to understand.

Indelible: Making marks that cannot be removed.

Illegible: Not clear enough to be read.

Incorrigible: Not able to be changed or reformed.

The idiom is incorrectly used in the sentence I and the correct idiom will be ‘bat an eye’.
Cross paths: encounter or meet someone by chance.
Bat an eye: to avoid expressing surprise, fear, or shock.
The usage of the idiom in statement II is absolutely correct.
Fall on deaf ears: to disregard or ignore.
The usage of the idiom in statement III is absolutely correct.
Clarion call: a clarion is a high-pitch bugle.
Hence, the correct answer is option D. 

Let us first learn the meanings of the given words:
Enhancement (noun): an increase or improvement in quality, value, or extent.
Modified (adjective): revised or changed.
Amendments (noun): a minor change or addition designed to improve a text, piece of legislation, etc.
Since the context is that the changes are in the bill, noun ‘amendments’ is the perfect fit contextually and grammatically.

Hence, the correct answer is option D.

The correct order will be:
The national unity of a free people → depends upon a sufficiently even balance of political power (R)→ against a revolutionary opposition that is irreconcilably opposed to it (S)→ to make it impracticable (P)→ for there to be an arbitrary administration. (Q)

We can say that ,
Use structure “auxiliary + past participle”
The above given sentence is given in Passive Voice :-
Wine should be opened about three hours before it is used.
Hence ,required answer will be option D .

According to the given context we are talking about the critics who always criticize people but they have not done the job themselves in life.

Back to square one: Returning to the place from where one started 

Close but no cigar: Being close to accomplishing a goal but only falling short at the end 

Crying wolf: Intentionally raising a false alarm 

Back seat drivers: People who criticize from the sidelines 

From all the given options, we can see that only option D fits in the given context since it expresses the correct meaning of the given statement.

This makes option D the correct choice among the given options.

The given sentence in active voice is: "Ads on TV increase the sale of any commodity."

The correct transformation of this sentence into the passive voice is: "The sale of any commodity is increased by ads on TV."

Therefore, the correct answer is option B: "The sale of any commodity is increased by ads on TV."

The correct answer is 4.4.

Key Points

• The formula to calculate the average of given numbers is equal to the sum of all the values divided by the total number of values.
• In MS-Excel the format of using the Average formula is
  • ​= Average(number1, number 2, number 3, .....).
• Here, the sum of numbers is 22 and this should be divided by 5.
• Hence the result is 4.4

Additional Information

• SUM(): This function is used to adds all the values within a cell range.
• ROUND(): The round function is used to round a number to a specified number of digits.
• RAND(): This function is used to returns a random number greater than or equal to 0 and less than 1.
• MOD(): This function is used to find the remainder after dividing a number by another number.

The correct answer is CTRL + N.

Key Points

• Create a new document with Ctrl+N. 

Additional Information

• Basic computer shortcut keys
  • Ctrl + M -- Indent the paragraph.
  • Ctrl + B -- Bold highlighted selection.
  • Ctrl + D -- Font options.
  • Alt + F--File menu options in the current program.
  • Alt + E--Edits options in the current program.
  • F1--Universal help (for any sort of program).
  • Ctrl + A--Selects all text.
  • Ctrl + X--Cuts the selected item.
  • Ctrl + Del--Cut selected item.
  • Ctrl + C--Copy the selected item.
  • Ctrl + Ins-- Copy the selected item.
  • Ctrl + V--Paste the selected item.
  • Shift + Ins -- Paste the selected item.
  • Home -- Takes the user to the beginning of the current line.
  • Ctrl + Home--Go to the beginning of the document.
  • End -- Go to the end of the current line.
  • Ctrl + End -- Go to the end of a document.
  • Shift + Home -- Highlight from the current position to the beginning of the line.
  • Shift + End -- Highlight from the current position to the end of the line.
  • Ctrl + (Left arrow) -- Move one word to the left at a time.
  • Ctrl + (Right arrow) -- Move one word to the right at a time.

The correct answer is a "Device driver".

Key Points

• The main job of the operating system is to manage all of the other application programs as well as build the communication between hardware and software,  in a system. The operating system uses a unique software program to perform such a task. This software program is known as the device driver.
• The program is written in the device driver software to control the specific hardware system attached to the computing device.
• The example of the device driver can Bluetooth or wireless network driver. 

Thus the correct answer is a Device driver.

Additional Information

• Memory buffer is referred to as a small memory container in the RAM. This memory buffer can hold the data temporarily. 
• Device port is a part of hardware where the user can insert cables to connect with other devices.

As Students read in College similarly Patients are treated in Hospital.

Logic: Synonymous Relationship.

Here,
Dawn : Sunrise → Dawn and Sunrise are synonymous because they both refer to the early morning time when the sun begins to rise.

Similarly,
Easy : Simple → Easy and Simple are synonymous because they both refer to something that is not difficult.

These are all defensive games.

As 'smoke' leads to 'pollution' in the same way ''War'' leads to 'destruction'.

The total distance = 15 + 20 + 30 + 15 = 80m

Hence, the correct answer is 80m.

= (5 + 4)km
= 9km
Required distance = AB
= (5 + 4)km
= 9 km