BEL Trainee Engineer Electronics Mock Test - 7 - Electronics and Communication Engineering (ECE) MCQ

Digital to Analog Modulation technique is as shown.

Important Points

1) As shown, QAM is a mixture of both ASK and PSK.

2) QAM uses two carrier signals with the same frequency but with which are in quadrature. Quadrature here means out phase by 90°.

3) Since the two signals have the same frequency, they are detected using synchronous detection.

4) Hence, amplitude and the phase of the carrier frequency both vary with the message signal.

A constellation diagram of a QAM signal with 2 different amplitude levels and 8 different phases is shown:

The non-linear device acts as frequency multiplier with appropriate bandpass filter, since y(t) = [x(t)]³ is the non-linear device, 3^rd harmonic with carrier frequency is possible i.e. f_C = 32.4 MHz

The high-power amplifier is used for the final power amplification of the digital RF signal in C-Band/Ku Band that is fed to the antenna.

The important parameters of the HPAs are:

• Frequency range
• Output power
• Bandwidth
• Gain Variation

The different types of HPA are:

• KHPA – Klystron HPA
• TWTA -Travelling Wave tube amplifier
• SSPA – Solid-state Power Amplifier

Out of these HPA, TWTA is used in broadcasting, radar and in satellite transponders.

Concept:

Johnson counter also known as creeping counter is an example of a synchronous counter.

In the Johnson counter, the complemented output of the last flip-flop is connected to an input of the first flip-flop, and to implement an n-bit Johnson counter we require n flip-flop.

Analysis:

The circuit diagram can be simplified at the block level as shown below

The initial state is given as 0000

After the 6th Clock, ABCD will be at 0011

Concept:

We know that:

• AND gate output is '0' (If any input is '0').
• AND gate output is '1' (If all inputs are '1').
• OR gate output is '1' (If any input is '1').
• OR gate output is '0' (If all inputs are '0').

Analysis:

In the given logic circuit:

Inputs: A, B, C, D

Output: x, y, z

Let us assume , name of AND gates are A₁,  A₂,  A₃

Solution:

Output of A₁ = 

Output of A₂ =

Output of A3 =

Output x =Output of A₁ +Output of A₂ 

Output y =Output of A2 +Output of A3 

Output z =Output of A3

 = A.B.C.D

Concept:

The concept of converting an analog signal to its digital counterpart is explained with the help of the following diagram:

∴ The maximum quantization is given as:

Δ = step size given by:

L = Number of levels

Calculation:

With n = 3, the number of levels will be:

L = 2³ = 8

With analog input in the range 0 to 8 V and L = 8, the step size will be:

Now, the maximum quantization error will be:

Concept:

The equivalent inductance for a coil is given by:

Case 1: For additive polarity

When the current either enters or leaves from both the windings of the coil, then the coil is said to be connected in additive polarity.

Case 2: For subtractive polarity

When the current enters from one winding and leaves from another winding of the coil, then the coil is said to be connected in subtractive polarity.

Explanation:

In the given circuit, the current is leaving from both the windings of the coil.

Hence, the coil is connected in additive polarity.

Concept:

• By shortening the length of the p-region the reverse recovery time (t_n) is reduced considerably.
• The stored charges can be reduced by adding gold dopants, thereby reducing storage time (t_s).
• Hence, gold dopants are also called lifetime killer.

Generally, T = T_n = t_s + t_t (t_s → storage time, t_t → transition time)

Also, frequency 

Hence, on reducing the storage time and reverse recovery time, the frequency is increased, thereby increasing the switching speed of the diode.

We know that,

Potential is given by

V = - 

dV = - E. dl cos θ 

|dV| = |E| |dl| cos θ 

if θ = 90° 

|dV| = |E| |dl| cos 90°  --------------------  (1)

|dV| = 0 -------------------    (2)

• Change in voltage zero i.e., voltage is constant.
• Surface with constant voltage is called equipotential surface.
• Actually ,meaning of (1) and (2) is when we move perpendicular to electric field voltage is constant. i.e, electric field and constant voltage surfaces are perpendicular.

Ethernet is a family of computer networking technologies commonly used in local area networks.

Token ring local area network (LAN) technology is a communications protocol for local area networks. It uses a special three-byte frame called a "token" that travels around a logical "ring" of workstations or servers.

Concept:

• Wavelength () is the distance over which the shape of wave repeats. 
• The relation between Wavelength () , Speed (v) and frequency (f) is 

                                    v = f 

Calculation:

Given; v = 0.7  C  ; here C is speed of light i.e is 3  10⁸ m/sec

           f = 1 Mhz = 1  10⁶ Hz

Hence, the answer is 210 m

Fibers that carry more than one mode are called multimode fibers. There are two types of multimode fibers:

1) Step Index

2) Graded Index

A comparison for step and graded fibers are respectively shown below:

We observe that in graded-index multimode optical fiber, the refractive index of the core is maximum at the fiber axis and decreases gradually towards the cladding.

Important Notes:

The multimode step-index multimode fiber suffers from Modal dispersion.

• Rays of light enter the fiber with different angles to the fiber axis. The limit is the fiber’s acceptance angle.
• Rays that enter with a shallow angle travel a more direct path and arrive sooner than those that enter at steeper angles.
• This arrival of different modes of light at different times is called modal dispersion.

Gas metal arc welding (GMAW) or Metal inert gas arc welding (MIG):

• In this process the arc is formed between a continuous, automatically fed, metallic consumable electrode and welding job in an atmosphere of inert gas, and hence this is called metal inert gas arc welding (MIG) process.

• The type of operation is generally used in GMAW is Semi automatic.

• MIG welding power sources control voltage; this is done by either voltage stepped switches, wind handles, or electronically.

• The amperage that the power source produces is controlled by the cross sectional area of the wire electrode and the wire speed, i.e. the higher the wire speed for each wire size, the higher the amperage the power source will produce.

• Argon is used in MIG welding as shielding gas.
• Argon is denser than air and settles over the joint to protect the molten pool from atmospheric gas contamination.
• In addition, argon is easy to ionize, so it handles a long arc at low voltages well.
• When the inert gas is replaced by carbon dioxide then it is called CO2 arc welding or metal active gas (MAG) arc welding.
• The common name for this process is gas metal arc welding (GMAW). 

Concept:

• Antivirus software, also known as anti-malware, is a computer program used to prevent, detect, and remove malware.
• Examples of common antivirus programs include MacAfee, Norton Antivirus, Kaspersky Anti-Virus, and Zone Alarm Antivirus.

Important Points

• Cipher: It is a method of writing in which a secret pattern of a particular set of letters or symbols is used to represent other letters, symbols, etc.
• Adware: It is also called advertising-supported software by its developers, is software that generates revenue for its developer by automatically generating online advertisements on users’ screen or installation process
• Firewall: It is a network security system that monitors and controls the incoming and outgoing network traffic based on predefined security rules

An ammeter is an electrical device that is used to measure the current.

In an ammeter, a low-value resistance is connected in series with it.

This is done to ensure a low voltage drop on the ammeter.

Values of input resistance

Concept:

A group of wires called bus is used to provide necessary signals for communication between modules. A bus that connects major computer components is called system bus. It connects the CPU, memory and I/O modules. System bus is divided further into three types: data bus, address bus and control bus.

Explanation:

Data bus: These are used to send data to memory and output ports and to receive data from memory and input port. These are bi-directional. The Communication between the components in a microcomputer takes place via the address and data bus.

Address bus: It is unidirectional in nature. Address is send from CPU to memory and I/O port.

Devious: behaving in a dishonesty way
Nefarious: criminal
Surreptitious: stealthily done : secretly done
Villainous: very evil and unpleasant

We don't get appropriate economic return because the quality is not as good as the original material.

The correct answer is ROM.

Key Points

• ROM
  • Read-Only Memory is a ROM in a computer.
  • Read-only memory is a storage medium that permanently stores data on computers and electronic devices.
  • The data stored in these chips is nonvolatile i.e. it is not lost when power is removed.
  • There are five basic ROM types:
    • ROM: Read-Only Memory.
    • PROM: Programmable read-only memory.
    • EPROM: Erasable programmable read-only memory.
    • EEPROM: Electrically erasable programmable read-only memory.
    • Flash memory: Flash memory, a type of EEPROM that uses in-circuit wiring. 
  • BIOS uses Flash memory.

Additional Information

• Register
  • The smallest and fastest memory of a computer is registered memory located in the computer's central processing unit(CPU).
  • It generally stores the most used instructions, data, etc. which are to be used by CPU.
  • Control Unit is part of the CPU.
  • It advises the input and output devices, and computer memory on how to respond to the instructions sent to the processor.
• RAM
  • It stores data that the computer needs to use temporarily. So it is faster than the secondary storage devices. It is a volatile memory i.e. the data disappear from it when the power is off.
  • It is known as the Read-Write Memory. i.e. the user can write information into RAM and read information from it.
  • It is called random access since any memory location can be accessed randomly for reading and writing. The access time is the same for each memory location.
  • It is usually called “temporary” memory, which means that when the system is shut down, the memory is lost.
• Cache
  • A cache memory is used by the central processing unit of a computer to reduce the average cost time or energy to access data from the main memory.
  • Generally Cache memory is logically positioned between CPU and main memory.

The correct answer is Pixels.

Key Points

Pixels

• The term pixel is actually short for Picture Element.
• These small little dots are what make up the images on computer displays, whether they are flat-screen (LCD) or tube (CRT) monitors. The screen is divided up into a matrix of thousands or even millions of pixels.
• A pixel is the smallest unit of a digital image or graphic that can be displayed and represented on a digital display device.
• A pixel is the basic logical unit in digital graphics. Pixels are combined to form a complete image, video, text, or any visible thing on a computer display.
• A pixel is also known as a picture element (pix = picture, el = element).

Additional Information

Dot pitch

• It is a specification for a computer display, computer printer, image scanner, or other pixel-based devices that describe the distance, for example, between dots on a display screen.

Dot mapping 

• It is a cartographic representation method to visualize quantitative absolute values.

​The correct answer is Charles Babbage.

Key Points

• Charles Babbage is considered the father of computers.
• Charles Babbage invented the machine called the Analytical Engine, which is a model of today's computers. Since he was the first person who gave us the basic idea of computers, he is known as the 'father of computers.
• In 1837 the Analytical Engine contained an ALU (arithmetic logic unit), basic flow control, and integrated memory, hailed as the first general-purpose computer concept.
• Because of funding issues, this computer was not built while Charles Babbage was alive. However, in 1910 Henry Babbage, Charles Babbage's youngest son was able to complete a portion of the machine that could perform basic calculations.
• Although Babbage never completed his invention in his lifetime, his radical ideas and concepts of the computer are what make him the father of computing.

Additional Information

Explanation:

• Integration: Integration refers to the process of combining or merging two or more software applications to work together.


• MS Word and Excel: MS Word is a word processing software, while MS Excel is a spreadsheet software.


• Client-Server Model: In computing, the client-server model is a distributed application structure that partitions tasks or workloads between the providers of a resource or service, called servers, and service requesters, called clients.


• Integrating MS Word and Excel: When integrating MS Word and Excel, the Word application is usually considered as the client.


• Functionality: MS Word acts as a client to request data or perform operations on the Excel application, which acts as the server.


• Examples: Some examples of integrating MS Word and Excel include importing data from Excel into Word for creating reports, generating mail merges using Excel as a data source, or embedding Excel charts or tables within Word documents.


• Benefits: Integrating Word and Excel allows users to combine the features of both applications to enhance productivity and create more comprehensive documents.

Therefore, the correct answer is C: Client.

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 option is (3)Select -> Delete

Key Points

• Click the arrow next to Delete in the Cells group on the Home tab, then select Delete Cells.
• Simply pick the cells you want to clear, then press Ctrl + Shift + Del on your keyboard to accomplish this. The selected cells' contents will be instantly cleared when you use this shortcut.
• Get rid of a worksheet
  Select with a right-click on the Sheet tab. Delete.
  Instead, you can choose the sheet first, then Home > Delete > Delete Sheet.
• The cells, columns, or rows that are chosen will be deleted if you press Ctrl + Delete. Shift + Delete: With this shortcut, you can delete a row, column, or set of cells while also moving the other cells to the right or left.
• Click Delete next to Remarks on the Review tab. As a hint, you can also remove a remark by using the close button in the comment balloon's upper right corner.
• Excel has two different cell deletion options: deleting just the cell's contents and deleting the entire cell. A cell, any selected row or group of rows, a random column, and the removal of formatting from a cell selection are all possible outcomes of the Delete operation.

Additional Information

• Select -> Esc: This shortcut does not perform any function. "Select" is not a valid key on a keyboard and "Esc" usually means "Escape" which is used to cancel a command or operation.
• Select -> Ctrl Select: This shortcut is used to select multiple non-contiguous pieces of text. You can hold down the "Ctrl" key on your keyboard and then click on different parts of the text you want to select. This allows you to select text that is not in a continuous block.
• Select -> Delete: This shortcut is used to delete the currently selected text. Once you have selected the text you want to delete, pressing the "Delete" key on your keyboard will remove it from your document.
• Select -> Alt: This shortcut does not perform any function. "Select" is not a valid key on a keyboard and "Alt" is usually used as a modifier key to access menu items or perform other shortcuts.

As 'Ophthalmia' is a disease of 'Eye' in the same way 'Rickets' is the disease of 'Bone'.

As 'Forest' and 'Vivarium' have the same meaning in the same 'Sea' and 'Aquarium' have the same meaning.

in the figure the 8 triangle is shown easily and another is COD , DOB, BOA, AOC, ACD, BDC,ABC, ABD so that total no. of triangle is 8 + 8 = 16

1) 8, 4, 3, 7, 1, 5, 2, 6

2) 5, 2, 7, 3, 4, 1, 8, 6

3) 3, 1, 6, 8, 4, 5, 2, 7

4) 1, 4, 8, 3, 2, 5, 7, 6

'POLITICS' is a meaningful English word.

Hence, '1, 4, 8, 3, 2, 5, 7, 6' is the correct answer.