BEL Trainee Engineer Electronics Mock Test - 10 - Electronics and Communication Engineering (ECE) MCQ

• Excess 3 code is a 4-bit code.
• It can be derived from the BCD code by adding ‘3’ to each coded number. Thus, in excess 3 code 0011 is added to each BCD number.
• It is an un-weighted code.
• It is a self-complimenting code i.e. the 1’s complement of an excess three number is the excess 3 code for the 9’s complement of the corresponding decimal number.

A programmable logic controller (PLC) or programmable controller is an industrial digital computer which has been adopted for the control of manufacturing processes, such as assembly lines, or robotic devices, or any activity that requires high-reliability control and ease of programming and process fault diagnosis.

Early (PLC) was designed to replace relay logic systems. These PLCs were programmed in "ladder logic", which strongly resembles a schematic diagram of relay logic.

The current gain β of the transistor is given by:

D_E: Diffusion constant of minority carriers in the emitter

D_B: Diffusion constant of minority carries in Base

N_E: emitter doping concentration

N_B: Base doping concentration

L_E: Length of diffusion of minority carriers in emitter

W_B: Base width.

 ratio of conductivity from emitter to base = 10 (Given)

LE_n (minority carries in emitter)  (hole diffusion length in base)

Taking the case of Si:

β = 2.1 × 10 × 5 = 105

Taking case of Si:

β = 2.6 × 10 × 5 = 130

None of the given option match, but if we check the option by satisfying the relation  

Only option 1 is satisfying

Hence option 1 is correct.

Concept:

The electric field for an isotropic antenna varies with the distance as given:

1/r term is the most dominant. 

Calculation:

Given,

E = 3 V/m for r = R

For r₂ = 3R,

Electric field E₂ will be 

Concept:

WBFM is given as:

Actual BW of WBFM is ∞ so to Bandlimit WBFM signal all of its significant lower-order sidebands retained and higher-order insignificant sidebands should be eliminated.

Calculation:

BW = 32 KHz

Given FM system has 8 sidebands (significant) i.e. 8 sidebands on the positive side of frequency & 8 sidebands on the negative side of the frequency

So, It has sidebands up to order ‘8’.

According to carson rule:

Significant sideband upto order of (β + 1) has B.W

BW = (β + 1) 2f­_m

So,

32 = 8 × 2 f_m

f_m = 2 kHz

Concept:

In an N-type semiconductor, the doping done is of pentavalent atoms.

As the doping density increases the Fermi level moves towards the conduction band.

If ND is the doping density, then the upward shift in the Fermi level is given by

From the expression

As ND increases  increases and the shift increases.

Calculation:

The electrostatic potential of n type semiconductor

E_F - E_i = qν_n

E_F - E_i = 0.359 eV

Concept:

If V₀ is the initial voltage across capacitor

Calculation:

Circuit diagram at laplace domain

As capacitor was initially relaxed: V₀ = 0 (Voltage source will be replaced by a short circuit)

Given;

C = 1μF

R= 5 Ω 

Use nodal analysis at node V_C

Determine the values of A and B using partial fraction

A_s=0 = (10/C)/(s + 1/RC) = (10/C)( 0 +1/RC) = 10R

B_{s= -1/RC} = (10/C)/s = -10R

⇒ V_C = (10R)/s + (-10R)/(s + 1/RC)

Using inverse laplace transform:

⇒ V_C = 10R -10Re^-t/RC

⇒ V_C = 10R(1 -e^-t/RC)

∴  V_C = 50(1 -e^-t/5)

Concept:

In IC fabrication it is difficult to fabricate capacitors due to the following reasons:

• A large area is required on the chip for a large value of the capacitor (in mF or μF).
• Leakage problem because dielectric is present between the plates of the capacitor.
• The speed of operation is reduced because the capacitor is an energy storage device.
• The cost of fabrication increased.

Fabrication of semiconductor device on the IC chip is more reliable because most of the semi-conductor devices are made-up of by silicon (Si)

Examples: Diode, Transistor, FET, MOSFET, CMOS

Resistors can also be fabricated on IC’s easily because it can be made by the semiconductor material.

Important Points

1) The small value of capacitors (in pF) can be fabricated on IC.

2) VLSI technology is used in the IC fabrication process.

Impulse function is exist only at t= 0 and the area under impulse function is unity

|_t=0 = 1

|_t=0 = 1

Discrete time Laplace transform is Z- transform.

The resistances are classified depending upon the values as:

• The resistances of the order of 1 Ω (or) less than 1 Ω are classified as low resistances.
• The resistances from 1 Ω to 100 KΩ are classified as medium resistances.
• The resistances of the order of 100 KΩ (or) higher are classified as high resistances.

The methods used for the measurement of low resistances are:

Kelvin's Double Bridge Method: Kelvin's Double Bridge Method is a modification of the Wheatstone bridge method. 

The circuit diagram is shown below:

R is the unknown resistance and S is the standard resistance.

Ammeter Voltmeter Method:

Connecting voltmeter across the load is suitable for low resistance measurements.

Ammeter reading is:

Voltmeter reading = E

The calculated resistance is:

Potentiometer Method:

• It works by comparing the unknown resistance with the standard resistance.
• The voltage drop across the known and unknown resistance is measured and by comparison the value of known resistance is determined.

Important Points

The author says that government has launched a number of schemes. But no solid step taken.

• Definition: A bootstrap is a small initialization program that starts up a computer system. It is responsible for loading and executing the operating system or other software components necessary for the system to function.


• Function: The bootstrap program resides in the computer's firmware or read-only memory (ROM) and is automatically executed when the system is powered on or restarted.


• Initialization: The bootstrap program initializes the hardware components of the computer, such as the processor, memory, and input/output devices.


• Bootloader: The bootstrap program then loads and executes a more complex bootloader, which further initializes the system and loads the operating system or other software from storage devices, such as hard drives or solid-state drives.


• Chain of Execution: The bootstrap process involves a chain of execution, where each component in the chain is responsible for loading and executing the next component until the operating system is fully loaded and running.


• Importance: The bootstrap program is crucial for the proper functioning of a computer system as it ensures that the necessary software is loaded and executed in the correct order.

The correct answer is Tab

Important Points

• Tab key should be pressed continuously while moving a column in MS Excel.
• Select the column that you want to move. Hold the Shift Key from your keyboard. Move your cursor to the edge of the selection.
• It would display the move icon (a four-directional arrow icon). Click on the edge (with the left mouse button) while still holding the shift key.
• Move it to the column where you want this row to be shifted.

Key Points

• Open a blank workbook on Excel and press the TAB key and your active cell should move to the column on the right. Hold in Shift and then press the TAB key and it reverses direction moving your active cell to the column on the left. You can also use this shortcut when tabbing through options in a dialogue box.
• Press the Enter key and your active cell should move to the row below. Hold in Shift and then press the Enter key and it reverses direction moving your active cell to the row above.
• 
• Using Shift and the arrow keys will select cells and using Shift when clicking on cells will select a contiguous cell range.

The correct answer is Ctrl + 3.

Key Points

The correct answer is a - ii, b - iii, c - iv, d - i.

Key Points

• Optical Mouse
  • It is a computer mouse that uses a light source, typically a light-emitting diode (LED), and a light detector, such as an array of photodiodes, to detect movement relative to a surface.
  • It uses special-purpose image processing chips, as the mouse takes over 1,000 images/ps below the surface level to detect movement through reflected light changes.
  • It uses camera technology and digital processing to compare and track the position of the mouse.
• Track Ball
  • ​It is an input device used to enter motion data into computers or other electronic devices.
  • It is designed with a moveable ball on the top, which can be rolled in any direction.
  • A moving ball is mounted on a stationary device that can be rotated mechanically (manually) using the fingers
• Digitizing(Graphic) Tablet
  • ​It is a computer input device that enables a user to hand-draw images, animations and graphics, with a special pen-like stylus.
  • Alternatively, it is a tool used to convert hand-drawn images into a format suitable for computer processing.
• Joystick
  • ​It is an input device that can be used for controlling the movement of the cursor or a pointer in a computer device.
  • It was first invented by C. B. Mirick at the U.S. Naval Research Laboratory, and patented in 1926.
  • It includes a base and a stick that can be move to the different direction.
  • It is used to indicate position in video game play.

Fragmentation is a common issue in memory management, where available memory becomes divided into small, non-contiguous blocks. This can lead to inefficient memory utilization and can negatively impact the performance of a system. The problem of fragmentation occurs in heap allocation due to the following reasons:

• Internal Fragmentation: This type of fragmentation occurs when allocated memory blocks have unused space within them. It happens because memory is allocated in fixed-size chunks, and if the requested memory size is smaller than the chunk size, the remaining space is wasted.



• External Fragmentation: External fragmentation occurs when free memory blocks are scattered throughout the heap, making it difficult to find contiguous blocks of memory for allocation. This can happen when memory blocks are allocated and deallocated in a non-sequential order, leaving gaps between allocated blocks.



• Compaction: Compaction is a technique used to reduce external fragmentation. It involves moving allocated blocks of memory closer together and filling the gaps left by deallocated blocks. However, compaction can be time-consuming and may require updating memory references, which can be challenging in systems with dynamic memory allocation.



• Allocation Policies: The choice of allocation policies can also contribute to fragmentation. For example, a first-fit allocation policy may result in more external fragmentation compared to a best-fit policy.

Overall, fragmentation in heap allocation can lead to inefficient memory usage, decreased performance, and increased memory overhead. It is important to consider fragmentation issues and employ appropriate memory management techniques to mitigate these problems.

The correct answer is .xlsx.

• .xlsx is the default XML-based file format for Excel 2010 and Excel 2007.
• Tar, Zip, rar are archive formats.

Additional Information

• An archive format is the file format of an archive file.
• Some file types and file extensions are as follows.

Given:

6% of √(3x) = 0.18

Concept:

Concept of percentage. It is calculated on the basis of 100

For example x% means x out of 100

Calculation:

According to the question,

⇒ 6% of √(3x) = 0.18

⇒ (6/100) × √(3x) = 18/100

⇒ √(3x) = 3

⇒ 3x = 3²

⇒ 3x = 9

⇒ x = 3

∴ Required value of x is 3.

The logic is :

1) BEH

2) KNR

3) GJM

4) TWZ

Hence, 'KNR' is the odd letter.

‘Knife’ is related to ‘Cut’, means we use knife for cutting.

Similarly,

We use pen for writing.

Hence, Write is the correct answer.

As 'Table' is made from 'Wood' in the same way 'Shirt' is made from 'Cloth'.

In the figure the simplest Triangles are GLK, DLJ, DJM,HMN,QRE,IRA,IPA, and FPO is the 8 triangle

and another is BDO,CDQ,DLM, PRA, KFI, NEI, HJI, GJI,DKI, and DNI is the 10 triangle

and another is DIE, DFI, DOA, DQA, and GHI is the 5 triangle

and DCA, DBA is the 2 triangle and DEF and ABC so that according to the figure the total no. of triangle is
8 + 10 + 5 + 2 + 1 + 1
= 27

The logic followed here is:

The figure in image 2 is water image of the figure in image 1. The figure in image C of answer figure will be the water image of the figure in image 3.

Hence, image C of answer figure is the correct answer.

From the final arrangement, we get V sits second to the right of S.
Hence, Option B is correct.
References:
Q sits second to the right of P.
Inferences:
From the above reference, we get two different cases:
In case 1, P sits at the corner or in the middle of the side of the table.

References:
R is not an immediate neighbor of P.
R faces inside.
R sits third to the left of W.
Inferences:
From the above references, we get different cases for R, in case 1(a) in which R faces P and in case 1(b) R faces Q.

References:
T sits third to the left of U.
V sits second to the left of U.
Inferences:
So, from this case 1(b) and case 2 will be eliminated as there is no possible place for V in these cases after placing U and T. Hence, we get our final arrangement in which S sits on the immediate left of P and V sits on the immediate right of R.
Final arrangement:

First and fouth letters are interchanged while second and third letters are interchanged.