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

In satellite communications the Doppler shift is given by  

where v is radial velocity of satellite, R_e is mean radius of earth, h is altitude of satellite, f_c is carrier frequency of signal and γ is elevation angle.

TTL (Transistor-Transistor Logic):

• A TTL input signal is defined as "low" when between 0 V and 0.8 V with respect to the ground terminal. 
• A TTL input signal is defined as "high" when between 2 V and 5 V.
• if a voltage signal ranging between 0.8 V and 2.0 V is sent into the input of a TTL gate, there is no certain response from the gate and therefore it is considered "uncertain" (precise logic levels vary slightly between sub-types and by temperature).

• TTL outputs are typically restricted to narrower limits of between 0.0 V and 0.4 V for a "low".
• TTL outputs are typically restricted to narrower limits of between 2.4 V and 5 V for a "high", providing at least 0.4 V of noise immunity.

Important Point

CMOS:

• For a CMOS gate operating at a power supply voltage of 5 volts,
• The acceptable input signal voltages range from 0 volts to 1.5 volts for a “low” logic state and 3.5 volts to 5 volts for a “high” logic state.
• Acceptable output signal voltages range from 0 volts to 0.05 volts for a “low” logic state, and 4.95 volts to 5 volts for a “high” logic state:

Cathode Ray Oscilloscope (CRO):

• The CRO stands for a Cathode Ray Oscilloscope.
• It is typically divided into four sections which are display, vertical controllers, horizontal controllers, and Triggers.
• Most of the oscilloscopes are used the probes and they are used for the input of any instrument.
• We can analyze the waveform by plotting amplitude along with the x-axis and y-axis.

• The applications of CRO are mainly involved in the radio, TV receivers, also in laboratory work involving research and design.
• In modern electronics, the CRO plays an important role in the electronic circuits.

Basic Controls of CRO: 

The basic controls of CRO mainly include position, brightness, focus, astigmatism, blanking & calibration.

• Position:
  • In the oscilloscope, the position control knob is mainly used for position control of the intense spot from the left side to the right side.
  • By regulating the knob, one can simply control the spot from left side to the right side.
• Brightness:
  • The ray’s brightness mainly depends on the intensity of the electron.
  • The control grids are accountable for the electron intensity within the electron ray.
  • So, the grid voltage can be controlled by adjusting the electron ray brightness.
• Focus:
  • The focus control can be achieved by regulating the applied voltage toward the center anode of the CRO.
  • The middle & other anodes in the region of it can form the electrostatic lens.
  • Therefore, the main length of the lens can be changed by controlling the voltage across the center anode.
• Astigmatism:
  • In CRO, this is an extra focusing control & it is analogous to astigmatism within optical lenses.
  • A ray focused in the middle of the monitor would be defocused on the screen edges as the electron path lengths are dissimilar for the center & the edges.
• Blanking Circuit: The time base generator present in the oscilloscope generated the blanking voltage.
• Calibration Circuit:
  • An oscillator is necessary for the purpose of calibration within an oscilloscope.
  • However, the oscillator which is used should generate a square waveform for preset

1) When the unwanted thermal noise exceeds the present threshold level, then false alarms are generated.

2) If the threshold is set too low, the large number of false alarms will mask the detection of valid targets. 

3) If the threshold is set too higher there will be very few false alarms, but it can inhibit the detection of valid targets.

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 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

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:

Optical fiber communication:

The communication system that uses lightwave for data transmission .

Optical fiber communication is carried out at a very high frequency 10¹⁴ to 10¹⁵ Hz. 

UltraViolet wave operates at 10¹⁴ to 10¹⁷.

Visible light band operates at 1014 to 1015.

Infrared band operates at 1013 to 1014.

Hence correct option is "4".

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

TDMA:

• Satellite communication among stations in different areas can be achieved if the satellite has the ability to switch time slots from one beam to another. This is known as time division multiple access (TDMA).
• In TDMA users transmit in rapid succession, one after the other, each using its time slots.

TSMA:

• The tone sense multiaccess protocol (TSMA) is designed for packet satellite communications.
• This protocol is particularly suitable for a satellite system serving an area with a dense population.

FAMA:

• In fixed- assignment multiple access (FAMA) channels are permanently assigned to terminals.
• Hence it is also known as a pre-assigned multiple access technique.

SCPC:

• Single-channel per carrier (SCPC) refers to using a single signal at a given frequency and bandwidth.
• Most often it is used as on broadcast satellite.

Inside a dynamic RAM chip, each memory cell holds one bit of information and is made up of two parts: a transistor and a capacitor.

• 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

The correct answer is option 2.

Key Points

• Serial Line Internet Protocol (SLIP) is a Data Link layer simple protocol that works with TCP/IP for communication over serial ports and routers. They provide communications between machines that were previously configured for direct communication with each other. 
• Border Gateway Protocol (BGP) is a Network layer used to exchange routing information for the internet and is the protocol used between ISP which are different ASes.
• User Datagram Protocol (UDP) is a Transport Layer protocol. UDP is a part of the Internet Protocol suite, referred to as UDP/IP suite. Unlike TCP, it is an unreliable and connectionless protocol.
• SNMP is an application layer protocol that uses UDP port number 161/162.SNMP is used to monitor the network, detect network faults and sometimes even used to configure remote devices

∴ Hence the correct answer is A-III, B -IV, C -II, D -I.

Additional Information

• Lament has two meanings out of which one is 'to complain'.
• Meaning of Complaint: a statement that something is unsatisfactory or unacceptable
• Meaning of Comment: a verbal or written remark expressing an opinion or reaction
• Meaning of Condone: accept (behaviour that is considered morally wrong or offensive)
• Meaning of Console: comfort (someone) at a time of grief or disappointment

According to the given context, it is clear that we are talking about the workers who are working tirelessly to finish an order since very little time is there for the company to get over with it.
 
A steal: A bargain that is very inexpensive 
 
Against the clock: Rushed and short on time 
 
All and sundry: Without making any distinction 
 
Add fuel to the fire: Whenever something is done in order to make a bad situation worse 
 
According to the given context, we can use option B in the blank here to express that the workers in the company are working very fast and tirelessly to deliver the order on time.

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

When air becomes heated. it becomes lighter.

The correct answer is F11.

• The F11 key can take our screen into and out of full-screen mode quickly and easily. 

​Important Points

Function key

A function key is a key on a computer or terminal keyboard which can be programmed so as to cause an operating system command interpreter to perform certain actions, a form of a soft key.

​Key Points 

         F11​

• The Most simple use is the F11 key can take our screen into and out of full-screen mode quickly and easily. 
• F11 key can be used by combined with Shift, Ctrl, Alt keys.

Some of the uses of the F11 key in MS Word.

• SHIFT + F11 = Go to the previous field.
• CTRL + F11 = Lock a field.
• CTRL + SHIFT + F11 = Unlock a field.
• ALT + F11 = Display Microsoft Visual Basic Code.
• ALT + SHIFT + F11 = Display Microsoft Visual Studio Code.

​Additional Information

        F8

• ​​We can access the menu by turning on your computer and pressing the F8 key before Windows starts.

        F9

• F9 will refresh fields in Word and prompt Outlook to send and receive messages.

        F10

• ​F10 activates the menu bar or Ribbon of an open application.
• Shift + F10 is the same as right-clicking on a highlighted icon, file, or Internet link. 

The correct answer is .

Key Points

• In MS Word, Shift- Ctrl - K is used for small-cap in MS Word.
• Other few common keyboard shortcuts used in MS Word are given below:
  • In MS Word, Shift- Ctrl - > is used to increase the font size in the document.
  • In MS Word, Shift- Ctrl - D is used to double-underline the selected content.
  • In MS Word, Shift- Ctrl-A is used to open the list bullet.

Additional Information

• The leading creators of MS Word software are Charles Simonyi and Richard Brodie, launched in 1983 under Microsoft corporation.
• Microsoft word is recognised as a word processor software which means that a user can rewrite, erase or modify a document as per the requirement.
• The documents created in MS Word are very high in quality. MS Word creates reports, stories, letters, resumes etc. 
• It allows users to edit or modify the new or existing document with colour or any other formats like bold, italic and underline. 
• In MS Word, the users can write the stories in paragraph format.
• The file extension used in Ms Word is .doc or .docx.

The correct answer is cell's column and row.

Key Points

• A cell reference or cell address is a combination of a column letter and a row number that identifies a cell on a worksheet.  
• For example, A1 refers to the cell at the intersection of column A and row 1; B2 refers to the second cell in column B, and so on.
• It is basically a cell's column number and row number.

Additional Information

• In MS Excel, columns are defined with Alphabets like A, B, C....and so on.
• While rows are defined with numerical values like 1, 2, 3, 4,.......and so on.

The correct answer is Second.

Key Points

• Second-generation computers (1955-1964) were made of transistors.
• The second generation of computers, which used transistors instead of vacuum tubes, were released in the late 1950s and early 1960s as interest in computer technology grew quickly.
• The second generation of computers, however, was entirely built using transistors rather than vacuum tubes.

Additional Information

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.

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".

As per the given information;

Distance between S and P = √(PQ² + QS²)
SP = √(6² + 8²)
SP = √(36 + 64)
SP = √100
SP = 10 km
Hence, S is 10 km in South-East with respect to P.

Checking Statement I:

Since there is no data given about Player and Champion, therefore, No player is Champion can not be derived.

Clearly, Statement I alone is not sufficient to answer the question.

Checking Statement II:

Statement II is the converse statement of the required conclusion.

Clearly, Statement II alone is sufficient to answer the question.

Hence, Option B is correct.

1st term = 1² = 1
2nd term = 2² = 4
3rd term = 3² = 9
4th term = 4² = 16
5th term = 5² = 25
Thus, Missing number = 6² = 36

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.