BEL Trainee Engineer Electronics Mock Test - 5 - Electronics and Communication Engineering (ECE) MCQ

Concept:

If we pass the input signal to a single T-flip flop, we will get half of the frequency at the output.

Similarly, when we pass the input signal to n-T flip-flops, the output frequency (f_out) will be:

Application:

Given Input frequency f = 200 Hz

f_out = 25 Hz

The frequency spectrum of an Amplitude Modulated wave is given by:

Bandwidth in AM = 2f_m = 6 kHz

f_m = 3 kHz

Upper sideband = f_c + f_m = 600 kHz

∴ The carrier frequency is:

f_c = 600 – f_m = 600 - 3 kHz

f_c = 597 kHz

• In electronics, a super-heterodyne receiver uses frequency mixing to convert a received signal to a fixed intermediate frequency (IF) which can be more conveniently processed than the original carrier frequency and audio stage does not need alignment in a radio receiver.
• Audio mixing is one of the applications where two different audio frequencies are mixed using super-heterodyne receiver. 

Concept:

The data flow between the two devices can be in simplex, half duplex and full duplex modes.

1. Simplex

• In Simplex, communication is unidirectional. Only one of the devices sends the data and the other one only receives the data.
• The channel capacity is used by only one device all the time.

Example: A CPU sends data while a monitor only receives data.

2. Half Duplex

• In half duplex both the stations can transmit as well as receive but not at the same time. When one device is sending other can only receive and vice-versa
• The channel capacity is shared by both the devices but at a time only once device uses the full capacity.

Example: A walkie-talkie

3. Full Duplex

• In Full duplex mode, both stations can transmit and receive at the same time.
• The channel capacity is shared by both communicating devices at all times.

Example: mobile phones

The modulation index,  for a Frequency modulated wave, is given by:

Δf = Frequency deviation

f_m = Modulating frequency

Calculation:

Given, Δf = 50 kHz and f_m = 100 Hz

β = 500

PWM :

It stands for pulse width modulation.

In this narrow or wide pulse is sent which means pulse width is varied.

For the generation of PWM 

• Comparator
• MonoStable Vibrator

Hence correct option is "4"

Concept:

The maximum range of a radar system is given as

Where:

R_max = Maximum range of the radar

S_min = Minimum Detectable Signal Power

P_t = Peak transmitted power

A_e = Aperture Area

D = Antenna diameter

We observe that 

Rmax ∝ D^1/2 x P_t^1/4  

Calculation:

P(new) = 16 P(old)

D(new) = 2D(old)

R_max ∝ D^1/2 x P_t^1/4  

R(new) = √2D^1/2 x 2P^1/4

R(new) = 2√2R(old)

R(new) = √8R(old)

Hence,  If the peak transmitted power is increased by a factor of 16, and the antenna diameter is increased by a factor of 2, the radar range will be increased by a factor of √8.

Concept:

R – 2R ladder DAC:

3 bit R – 2R DAC  by using Inverting op-amp is shown below:

Output voltage is defined as:

V₀ = - I₁(R_F) ⋯ (i)

Current is calculated as:

     ⋯ (ii)

Current drawn from the source is

I = V / R ⋯ (iii)

Current is calculated as:

The final output voltage is

For n bit DAC output voltage is

Calculation:

Given digital input is 1010 and the reference voltage is 5 V

a₃ = 1, a₂ = 0, a₁ = 1, a₀ = 0

considering the value of the feedback resistor for Op amp is R Ω

Output voltage is

V₀ = -3.125 V

Advantages and disadvantages of step-index mono-mode optical fiber.

Concept:

1. Optical fibres can be used to transmit light and thus information over long distances. The electromagnetic spectrum is composed of visible and near-infrared light like that transmitted by fibre, and all other wavelengths used to transmit signals such as AM and FM radio and television.

For fibre optics with glass fibres, we use light in the infrared region which has wavelengths longer than visible light, typically around 850, 1300 and 1550 nm.

2. Radar is a detection system that uses radio waves to determine the range, angle, or velocity of objects.

Radio waves (pulsed or continuous) from the transmitter reflect off the object and return to the receiver, giving information about the object's location and speed have frequencies as high as 300 gigahertz (GHz) to as low as 30 hertz (Hz). X-band is a segment of the microwave radio region of the electromagnetic spectrum, within the frequency range 8–12 GHz.

3. Sonar is a system used for the detection of objects under water by emitting sound pulses and detecting or measuring their return after being reflected.

Ultrasonic waves (sounds having frequency greater than 20,000 Hz) are used in sonar because Ultrasonic waves can penetrate water to long distances (because of their high frequency and very short wavelength), but ordinary sound waves or infrasonic waves cannot penetrate water to such long distances.

4. A mobile phone receives microwave signals from a nearby phone (or transmitter) and sends microwave signals back. These short bursts of microwave radiation can transmit a lot of information in a very short time with frequencies between 300 MHz (1 m) and 300 GHz (1 mm).

Therefore, the correct matched pairs are

Sensitivity of measuring instrument

• All calibrations and specifications of an instrument are only valid under controlled conditions of temperature, pressure, and so on. These standard ambient conditions are usually defined in the instrument specification.
• As variations occur in the ambient temperature, certain static instrument characteristics change, and the sensitivity to disturbance is a measure of the magnitude of this change.
• Such environmental changes affect instruments in two main ways, known as zero drift and sensitivity drift.
• Zero drift or bias describes the effect where the zero reading of an instrument is modified by a change in ambient conditions. This causes a constant error that exists over the full range of measurement of the instrument. 
• Sensitivity drift defines the amount by which an instrument's sensitivity of measurement varies as ambient conditions change. It is quantified by sensitivity drift coefficients that define how much drift there is for a unit change in each environmental parameter that the instrument characteristics are sensitive to. 

Schottky Diode:

It is not a typical diode because it does not have a p-n junction.

Instead, it consists a doped semiconductor (usually n-type) and metal, bound together as shown:

• When the metal comes into contact with n-type semiconductor the majority carriers, electrons, are infused into metal commonly called "Hot carrier" since injected electrons from semi-conductor have very high kinetic energy compared to electrons in a metal.
• ​The Schottky diode’s significant characteristic is its fast switching speed as it doesn't allow the diode to reach saturation.
• This makes the Shottky diode useful for high-frequencies and digital applications.
• Schottky diode is also known as the Schottky barrier diode, surface barrier diode, majority carrier device, hot-electron diode, or hot carrier diode.
• Its symbolic representation is as shown:-

          1

• The Schottky diode is a semiconductor formed by the junction of a semiconductor with metal. It has a low forward voltage drop and near-zero reverse recovery time hence used in very fast switching circuits.
• Schottky barrier diode can be used as a low noise amplifier due to metal-semiconductor junction.

Differential pulse-code modulators:

• The DPCM module implements one of the simplest compression algorithms.
• It combines a spatial prediction loop with a non-uniform quantizer of which the representation levels are Huffman encoded.
• It is a signal encoder that uses PCM but adds some functionalities based on the prediction of the samples of the signal.
• The input to the DPCM can be an analog or digital signal.
• The number of encoded bits is smaller than in the PCM system.
• It needs far fewer bits per error sample than what would have been needed for the original samples themselves.
• This results in fewer bandwidth requirements by the DPCM system and hence has a lower dynamic range than the original message itself.​

Hence, options 1 and 2 are correct.

Porous means (of a rock or other material) having minute interstices through which liquid or air may pass

Synonyms: permeable, penetrable, pervious
For instance, the new moonlet might be porous, like an orbiting icy rubble pile
Very high capacity supercapacitors use a porous carbon-based electrode material

• User data


• System data


• User program


• System stack

• User data: This includes the data that is specific to the user and is used by the user program.


• System data: This includes the data that is used by the operating system to manage the process, such as process control block (PCB), process state, priority, etc.


• User program: This is the actual program code that is executed by the processor.


• System stack: This is the stack used by the system for managing function calls and local variables.

The hardware used for calculating a Cyclic Redundancy Check (CRC) typically includes:

• An XOR unit to perform bitwise exclusive OR operations.
• A shift register to shift bits, which helps in the calculation of the CRC.

These components work together to efficiently compute the CRC value, ensuring data integrity in digital networks and storage devices.

The correct answer is Ctrl + Z.

Key Points

• Undo is a technique or a command which is implemented in many computer programs.
• It erases the last change done to the document.
• We can undo, redo, or repeat many actions in Microsoft Word, PowerPoint, and Excel.
• With the help of undo command, the users can explore and work without fear of making mistakes, because changes can be made whenever required.
• The opposite of undo is Redo.
• The redo command reverses the undo command.
• In Microsoft Windows applications, the keyboard shortcut for the Undo command is Ctrl+Z or Alt+Backspace, and the shortcut for Redo is Ctrl+Y or Ctrl+Shift+Z.

The correct answer is the Presentation program.

Key Points

• Microsoft PowerPoint
  • It is a powerful slide show presentation program. Hence, Option 4 is correct.
  • It is a standard component of the company's Microsoft Office suite software and is bundled together with Word, Excel, and other office productivity tools.
  • The program uses slides to convey information rich in multimedia.

Additional Information

Name Box: This is a small rectangular box located in the top left corner of the Excel window, to the left of the formula bar. It displays the address of the currently selected cell (for example, "A1" if the first cell is selected). Apart from displaying cell references, you can use it to define names to cells or ranges.

Formula Bar: This is located just below the ribbon and to the right of the name box. It is used to enter or edit a formula, a function, or data in a cell. It displays the contents of the currently active cell and allows you to create and edit formulas.

Status Bar: This is located at the bottom of the Excel window. It provides various types of status information, including the average, count, and sum of selected numbers, whether the scroll lock is on, and other status messages. It doesn't display the address of the selected cells.

Title Bar: This is at the very top of the Excel window, displaying the name of the currently open workbook (Excel file). The title bar is largely used to move the application window around and doesn't show the address of the selected cells.

Among these options, only "Name Box" displays the reference of the currently selected cell or cells.

According to the information given in the question, we can draw the following diagram.

Thus we can see if a man has to travel to point E from point A  (through these points by the shortest distance), he has to follow a path point A → B → F → E.

Thus travelling from point A, he will pass the first point B.

Hence, the correct answer is "Point B".

The logic is:

Column 1: 9 × 5 × 3 = 135

Column 2: 5 × 7 × 4 = 140 

Similarly,

Let the missing number in column 3 be 'a'.

So, 5 × a × 5 = 150

⇒ 25 × a = 150

⇒ a = 150 ÷ 25

⇒ a = 6

Hence, ‘6’ is the correct answer.

27 → 3³; 125 → 5³; 64 → 4³

Therefore ? = 6³ = 216.

Clearly, each word is coded by the numeral which is 1 less than the number of letters in the word.
Since, there are 10 letters in the word GOVERNMENT, so required = 10 – 1 = 9.
Hence, option C is correct.

Kanti is the niece of Suman.
Suman is the uncle of Kanti.
Prema is Suman’s mother.
Prema is grandmother of Kanti.
Harish is Prema’s father.
So, Kanti is the great-granddaughter of Harish.

P, Q, R, S, T, V, W, and Z are sitting around a circle facing at the centre not necessarily in this same order.

i) T is second to the right of R who is third to the right of P.

Mistake Points

Who is used for the second person in a connecting statement.

For example: 

T is second to the right of R who is third to the right of P.

Here, who is used for R and not for T.

ii) S is second to the left of P and fourth to the right of Q.

iii) V who is not an immediate neighbour of P. (This means V cannot sit immediate left or right of P).

iv) Z is third to the right of V 

Thus we can see R is second to the right of W

Hence, the correct answer is "Option 1".