BEL Trainee Engineer Electronics Mock Test - 2 - Electronics and Communication Engineering (ECE) MCQ

Process control system

An automatic control system in which the output is a variable is called a process control system.

An automatic control system is also known as a closed-loop system because the feedback will automatically correct the change in output due to disturbances.

An example of a basic process control system is a thermostat, a heating element, and a cooling element within a room. As the temperature in the room fluctuates beyond set boundaries, the thermostat turns on either the heating or cooling system to keep the room at a specific temperature.

Concept:

AM modulated wave equation:

 + 

Application:

Comparing the standard general spectrum to given spectrum

Since the question is asking about the percentage depth of modulation, it will be 80%

• A standing wave is defined as one whose magnitude does not change at certain points on a line while changing at other points.
• The variation of voltage or current with time gives an indication of a “stationary” wave vibrating at fixed locations, hence it is called a standing wave.
• Full standing wave on a half-wave open transmission line is given by:

• Clearly, at nodes, the voltage or current are respectively zero.

• Message: The message is the information (data) to be communicated; Popular forms of information include text, numbers, pictures, audio, and video
• Sender: The sender is the device that sends the data message; It can be a computer, workstation, telephone handset, video camera, and so on
• Receiver: The receiver is the device that receives the message; It can be a computer, workstation, telephone handset, television, and so on
• Transmission medium: The transmission medium is the physical path by which a message travels from sender to receiver; Some examples of transmission media include twisted-pair wire, coaxial cable, fiber-optic cable and radio waves
• Protocol: A protocol is a set of rules that govern data communication

Formula Used:

Pinch off voltage (VP) = 

Application:

Given,

a = 3 × 10-4 cm

ND = 1015 electron/cm3

ϵ = 12ϵ0

q = 1.6 × 10^-19 C

From above concept,

V_P = 

Where, 

After solving it,

V_P = 6.8 V

EXPLANATION:

Faraday’s Law states that a change in magnetic flux induces an emf in a coil.

Also, Lenz’s Law states that this induced emf produces a flux which opposes the flux that generates this emf, i.e.

     ----(1)

EMF is also defined as:

Also, 

Putting the above in Equation (1), we get:

Additional Information

Maxwell's Equations for time-varying fields is as shown:

The correct answer is option 1):(Reversed biasing)

Concept:

Diode

A diode is a semiconductor device that essentially acts as a one-way switch for current.

It allows current to flow easily in one direction but severely restricts current from flowing in the opposite direction

The reverse bias of the diode

• When an external voltage (V ) is applied across the diode such that the n-side is positive and the p-side is negative, it is said to be reverse-biased.
• The applied voltage mostly drops across the depletion region. The direction of the applied voltage is the same as the direction of barrier potential.
• As a result, the barrier height increases, and the depletion region widens due to the change in the electric field.
• When a diode is given an external voltage that increases its potential barrier and restricts the flow of current.

Additional Information
Forward biased diode:

• In the forward bias, the p side of the diode is connected to the positive side of the battery and the n side is connected to the negative side of the battery.
• The direction of the applied voltage is opposite to the junction barrier potential. Therefore, the size of the depletion region decreases.

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

Full Duplex

In Full duplex mode, both stations can transmit and receive at the same time.

Example: mobile phones

Important Points

Simplex

In Simplex, communication is unidirectional. Only one of the devices sends the data and the other one only receives the data.

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

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

Example: A walkie-talkie.

The correct answer is Magnetic Tape.

• Magnetic tape is a secondary storage device used for storing files of data; Example: a company’s payroll record.
• Access is sequential and consists of records that can be accessed one after another as the tape moves along a stationary read-write mechanism
• A hard disk is an electromechanical data storage device from which data is accessed in a random-access manner, individual blocks of data can be stored or retrieved in any order
• Both sequential and random access of data is possible in hard disk
• In random-access memory (RAM) the memory cells can be accessed for information transfer from any desired random location
• That is, the process of locating a word in memory is the same and requires an equal amount of time no matter where the cells are located physically in memory; Hence RAM is random access

Concept:

The cutoff frequency for dominant mode is given as:

a and b are the dimensions of the waveguide

Calculation:

The mode of operation is TE₁₀, i.e. m = 1, n = 0.

The cut off frequency for this mode will be:

f_c (1, 0) = 2.5 GHz.

Since 2.5 GHz is the cut-off frequency for TE₁₀ mode to operate, signals with frequencies below 2.5 GHz will not be able to pass.

Figure of merit (FOM):

A figure of merit is used to decide the quality of a communication technique

For Angle modulation:

FOM of FM is given by,

Thus, as transmission bandwidth W is doubled, FOM becomes one fourth.

Important Point

For Amplitude modulation:

The signal to noise ratio at output Is a maximum 1/3 (for μ = 1) of the signal to noise ratio at the input.

FOM is 1 for DSB, SSB, VSB.

​Phase Modulation:

According to the maximum power transfer theorem, to obtain maximum power from a source with finite impedance, the impedance of the load must be equal to source impedance.

Derivation:

From the above circuit, the current flowing through the load, ‘I’ is given as

Power transferred to the load,

In the above equation, R_L is a variable, therefore the condition for maximum power delivered to the load is determined by differentiating load power with respect to the load resistance and equating it to zero.

⇒ (R_L + R_TH)² = 2R_L (R_TH + R_L)

⇒  R_L + R_TH = 2R_L

⇒ R_L = R_TH

The correct answer is option 4):(the same as that of Y)

Concept:

• The given circuit resembles the wheat stone bridge
• 
• The Wheatstone bridge works on the principle of null deflection, i.e. the ratio of their resistances is equal, and no current flows through the circuit. Under normal conditions, the bridge is in an unbalanced condition where current flows through the galvanometer. The bridge is said to be balanced when no current flows through the galvanometer.
• If the resistance of each resistor is 100 ohm, The bridge is at balance condition no current flows in the centre arm. the potential at X is equal to y

Option 4 is correct:

Definitions:

A memory that can retain the data even if the memory is not connected with the power supply is known as non-volatile memory.

A memory that loses data if the power supply is disconnected is called volatile memory.

Additional Information 

• The flash memory belongs to the non-volatile memory group as it can store data for a permanent time. Examples of flash memory are BIOS chips.
• ROM stands for read-only memory, and it is permanent storage where once the stored is stored then it cannot be updated or erased. An example of ROM is a controller chip used in electronic devices that defines its functioning.
• Hard Drive is a storage memory that is used as a secondary memory in computers. It stores data for a permanent time. But the data can be altered and erased as per the user requirement.

According to Thevenin’s theorem, any linear circuit across a load can be replaced by an equivalent circuit consisting of a voltage source V_th in series with a resistor R_th as shown:

Vth = Open circuit Voltage at a – b (by removing the load), i.e.

If a linear circuit contains dependent sources only, i.e., there is no independent source present in the network, then the open-circuit voltage or Thevenin voltage will simply be zero. (Since there is no excitation present)

Important Point

Various Theorem and the circuits where they are applicable is shown below in the table:

• The File Transfer Protocol (FTP) is a standard network protocol used for the transfer of computer files between a client and server on a computer network
• Simple Network Management Protocol (SNMP) is an Internet Standard protocol for collecting and organizing information about managed devices on IP networks and for modifying that information to change device behaviour
• The Simple Mail Transfer Protocol (SMTP) is a communication protocol for electronic mail transmission
• Radio Free Ethernet (RFE) is a network audio broadcasting system, It consists of programs and tools that allow packets of audio data to be transmitted around a network

Notes:

• FTP is Transport layer protocol
• SNMP, SMTP is an application layer protocol

Over dry land, the air becomes very hot & when the Sun goes down it cools off quickly

The correct answer is option 4, i.e., They help you to club a group of commands and run them one after another

Additional Information

• A batch file is a text file that contains a sequence of commands for a computer operating system. It's called a batch file because it batches (bundles or packages) into a single file a set of commands that would otherwise have to be presented to the system interactively from a keyboard one at a time.
• Its extention is .bat.

An address of a website on the internet is called a URL.

Key Points

• URL stands for Uniform Resource Locator and is used to specify addresses on the World Wide Web.
• A URL is the fundamental network identification for any resource connected to the web (like images or sound files).

A URL has the following format:

Additional Information

1. Protocol:

• The protocol specifies how the information from the link is transferred. The protocol used for web resources is HyperText Transfer Protocol (HTTP).
• The protocol is followed by a colon, two slashes, and then the domain name
•  The domain name is the computer on which the resource is located.
• Links to particular files are specified after the domain name as shown above in the format.

2. Client:

• In computing, a client is a piece of computer hardware or software that accesses a service made available by a server as part of the client–server model of computer networks.

3. WAN:

• A wide area network (WAN) is a telecommunications network that extends over a large geographic area for the primary purpose of computer networking.

The correct answer is Open Source Software.

Key Points

• Open-source software is computer software that is released under a license in which the copyright holder grants users the rights to use, study, change, and distribute the software and its source code to anyone and for any purpose.
• Examples: GNU/Linux, Mozilla Firefox, VLC media player.

Additional Information

• Proprietary software is owned by an organization or an individual.
• Free software or libre software is computer software distributed under terms that allow users to run the software for any purpose as well as to study, change, and distribute it and any adapted versions.
• Unlicensed Software is software for which the trust or user does not possess a licence and therefore has no legal entitlement to use.

In the question, We have to find the common to all three figures which is shown below-

Here, The highlighted area is common to all shapes.

Hence, Option (3) is correct.

From Statement 1:

We have, D moved a distance of 40m towards north.

From there he turns to the right and walked for 30m and reached school.

Here, we can’t determine in which direction is D’s home from the school.

From Statement 2:

We have, D is facing south. He turns right and walk for 100m.

After that he turned to the left walk for 50m and reach home.

Here, we can’t determine in which direction is D’s home from the school.

Hence option B is correct.

Only daughter of woman’s father is woman herself. So, the woman is person’s mother.

Venn diagram according to the given information is:

Guava, Mangoes, Fruits

As Mangoes and guava both are fruits, so they will come inside the fruits.

But,

Individually both the guava and mangoes are different fruits so there will be no intersection or shared part, so they will come as a separate circle inside the fruits.

Hence, the correct answer is "Option 4".

From the common explanation, we get the position of G is 3rd to the right of C.

Hence, Option B is correct.

Common Explanation:

References:

One person sits between A and C, who sits second to the right of H.

G sits opposite to B.

Both G and B do not sit immediate left of H.

Inferences:

From the above reference, we get two different cases:

References:

D sits second to the left of B.

A doesn’t sit beside D.

E doesn’t face C.

Inferences:

From the above reference, case 1 will be eliminated because A doesn’t sit beside of D.

So, the final arrangement:

To solve the analogy problem where the pattern needs to be identified, let’s break it down step-by-step:

The analogy given is: 16 : 56 :: 32 : ?

We need to find the relationship between the numbers 16 and 56 and then apply that relationship to 32 to find the missing number.

1. Find the relationship between 16 and 56:

   • Step 1: Check the operations or patterns. Consider possible operations like addition, subtraction, multiplication, or division.

   • Step 2: Test if multiplication could be a pattern:

     16×3.5=56

     This works as:

     16×3.5=56

     Thus, multiplying by 3.5 seems to be the pattern.

2. Apply the same pattern to 32:

   32×3.5=112

   Therefore, according to this pattern, the number that replaces the question mark should be 112.

3. Verify the other options:

   • 96: This is much larger than expected.
   • 112: Also too large.
   • 121: Similarly, too large.
   • 128: While close, it’s not the result from our multiplication pattern.

Hence, the correct answer is:

112

In this figure counting the squares and we get the 27 squares.

From statement I alone, we don’t get the answer.

From statement II alone, Q is sitting 2nd to the left of T. T is facing P. The number of friends sitting between P and Q is same as the number of friends sitting between P and W.

From statement II alone, we don’t get the answer.

Combining both statement I and II, we get,

From statements I and II together, we don’t get the answer.

Hence, option ‘D’ is correct.