BEL Trainee Engineer Electronics Mock Test - 6 - Electronics and Communication Engineering (ECE) MCQ

Photodiode:

• A photodiode can convert light into either current or voltage depending upon the mode of operation.
• It is designed to operate in reverse bias.

Advantages of Photodiode:

• The photodiode is linear
• Low resistance
• A very good spectral response
• Better frequency response
• Low dark current
• Fastest photodetector
• It can be used as a variable resistance device
• Long lifetime, Low noise, High quantum efficiency, It is highly sensitive to the light
• Compact and lightweight
• No high voltage requires
• Using photodiode the speed of operation is very high

Disadvantages of Photodiode:

• Require increases in the dark current
• It depends on the temperature
• Small active area
• Normal PN junction photodiode has a very high response time
• It has very low sensitivity
• Light sensitive device
• Poor temperature stability

The correct answer is (option 4) i.e. 0 A

Concept:

• We have taken the example of A.C. the bridge here.
• Here we can clearly see that there are a total of 4 arms and one detector connected.
• For a balanced bridge, the detector shows zero deflections.

The condition for the balanced bridge is

So if the ac bridge is balanced, then the current through the detector is 0 A.

Additional Information

Concept:

The time constant for an RC circuit is given by:

τ = R_eq C

While calculating the time constant, independent must be replaced by their internal impedances.

Calculation:

R_eq = 1+ 2 Ω

R_eq = 3 Ω

τ = 3 × 1

τ = 3 sec

Additional Information 
The time constant for an RL circuit is given by:

Concept:

The probability of bit error is proportional to the distance between the closest points in the constellation diagram.

The bit error decreases as the distance increases.

Application:

Since the Probability of error is the same in both cases, the minimum distance must equal for the given pair of signal points.

For the first constellation, the minimum distance between two adjacent signal points is 2A.

For the second constellation, the minimum distance is:

Equating the two distances, we get:

4 A² = A₁²  + A₂² 

Also, the average Power in QPSK will be:

Average Power in QAM

⇒ 2A²

Hence Average power is the same in both diagrams.

A practical voltmeter must have a very high input resistance value (Ideally Infinite).

A voltmeter measures the voltage difference between the two different points but it should not change the amount of current going through the element between these two points.

So it should have high resistance so that it doesn't draw current through it.

Values of input resistance

Cleavage plane:

• When a crystal is break or fracture easily along a definite plane then this plane is called cleavage plane.
• It is used to identity mineral and its quality.
• It forms generally in a lower energy crystal structure.
• In silicon, most preferred cleavage plane is < 111 >

Silicon have two cleavage plane < 111 > and < 110 >

The correct answer is option 4.

Concept:

Options verify the best way to solve the problem.

Option 1: 8, 11

703x (in base-x number system) = 504y (in base-y number system)

703_x=504_y

(703)₈=(504)₁₁

451=609

LHS is not equal to RHS.

Option 2: 12, 13

703x (in base-x number system) = 504y (in base-y number system)

703x=504y

(703)₁₂=(504)13

1011=849

LHS is not equal to RHS.

Option 3: 17, 18

703x (in base-x number system) = 504y (in base-y number system)

703x=504y

(703)17=(504)18

2026 =1624

LHS is not equal to RHS.

Hence the correct answer is None of these.

Concept:

The numerical aperture of fiber optic cable is given by 

Where n1 and n2 are core and cladding refractive indices

Discrete fourier transform (DFT) is basically a fourier transform of “Sampled signal repeated periedically”.

The no. of points in DFT is known as N-point DFT. Which is crual to period of time domain signal.

If x[n] is sampled time domain signal, then its corresponding DFT X[k] can be expressed as:

Where N is period of x[n]

For a particular value of “k” there is (N – 1) complex addition and N complex multiplications takes place.

For one-point DFT = (N – 1) additions takes place

Then for N point DFT = (N)(N – 1) additions takes place

For one-point DFT, N multiplications takes place

Then for N point DFT, N² multiplication takes place.

Doppler Shift:

If the observer is moving with respect to the source he observes a change in frequency of the wave emitted by the source, this is called Doppler shift or Doppler effect.

f_d = doppler frequency in Hz

v = speed of wave source (m/sec)

λ = Wavelength (m)

Concept:

• An optical time-domain reflectometer (OTDR) is an optoelectronic instrument used to characterize an optical fiber.
• The Optical Time Domain Reflectometer (OTDR) is useful for testing the integrity of fiber optic cables.
• OTDR is used to verify splice loss, find faults, and measure the length of optical communication.
• The instrument emits short laser pulses, e.g. with pulse durations of some tens of nanoseconds and peak power of a few hundred milliwatts, as can be obtained with a single-mode laser diode.
• The pulses are injected through a launch cable into the tested optical fiber.
• Any reflected light is extracted with a directional fiber coupler and sent to a fast and sensitive photodetector.
• The photodetector allows for the time-resolved measurement of the reflected optical power and thus of the return loss.
• One can find the propagation losses and also find whether the loss coefficient is constant along with the fire or changes locally. 

The correct answer is option 2.

Concept:

  Registers are a type of computer memory used to quickly accept, store, and transfer data and instructions that are being used immediately by the CPU. The registers used by the CPU are often termed Processor registers.

A list of some of the most frequent registers found in a basic computer follows:

Hence the correct answer is PC.

Torque in measuring instruments

Following are the types of torque produced in measuring instruments.

1.) Deflecting torque

• This torque causes the pointer to move from its initial (zero) position.
• To obtain this force in an instrument, different effects of electric current are used such as magnetic effect, heating effect, chemical effect, etc.

2.) Controlling torque

• The controlling force always acts in opposite direction to the deflecting force.
• In absence of controlling torque, the pointer will swing beyond its final steady-state position and the deflection will be indefinite.
• After the removal of the moving mechanism, the pointer has to come back to its initial position, but in absence of controlling torque, the pointer won't come back to its initial position.
• The controlling force could be produced by spring or gravity control.

3.) Damping torque

• This torque is necessary to bring the pointer to rest in its final deflected position quickly.
• Without such damping, the combination of deflecting torque and controlling torque makes the pointer oscillate about its final deflected position for some time.
• The methods to produce damping torque in different instruments are:

Concept:

Lockout free condition: If a counter from an unused state enters one of the used states then the counter is called lock-out free. While taking any unused state as the initial state if the next state comes out to be a used state, the counter is said to be lockout free.

Synchronous counter: A counter in which all the flip-flops are triggered with the same clock pulse. In such counters, if the propagation delay of one flip-flop is tf, then the propagation delay for the whole counter will also be tf

Asynchronous counter: A counter in which all the flip flops are not triggered by the same clock pulse. In such counters, total propagation delay will be equal to the sum of propagation delay for all flip flops.

Calculation:

Given that, propagation delay of each flip-flop = 40 ns

Width of the strobe pulse = 20 ns

Total propagation delay = 40 × 4 + 20 = 180 ns

Maximum clock frequency 

The correct phrasal verb with verb ‘stem’ is ‘stem from’.

Stem from: to be caused by (something or someone).

Ex: Most of her health problems stem from an accident she had when she was five.

Hence, option A is correct.

Note :- Rule to make active voice of Simple Past Tense
We can say that ,
The above given sentence is given in Passive Voice :-
Use structure “subject + auxiliary + past participle + by + object”
That watch was stolen by him.
Hence , required sentence is option A .

The author makes this clear in the fourth sentence of the passage that a man of knowledge possesses immense influence in society

Definition of an Extranet:
An extranet is a private computer network that allows authorized users from different organizations to access shared information, collaborate, and communicate securely over the internet.
Explanation:
The correct answer is B: The intranets of two co-operating organizations interconnected via a secure leased line.
- An extranet is an extension of an organization's intranet, which is a private network accessible only to employees or members of the organization.
- It is used to provide controlled access to external parties such as suppliers, partners, or customers.
- The extranet allows these external parties to connect to the organization's intranet and access specific resources or information based on their authorization level.
- The connection between the two intranets is established via a secure leased line, ensuring the confidentiality and integrity of the data transmitted.
- The extranet provides a secure and collaborative environment for organizations to share data, documents, and applications with their trusted partners, suppliers, or customers.
- It enables efficient communication, streamlined business processes, and improved collaboration between organizations.
Key Points:
- An extranet is a private computer network.
- It allows authorized users from different organizations to access shared information.
- It enables collaboration and communication securely over the internet.
- It is an extension of an organization's intranet.
- It connects the intranets of two cooperating organizations.
- The connection is established via a secure leased line.

The correct option is (2) ".wav and mid files"

Key Points

• The following sound effects are available for Microsoft PowerPoint: A PowerPoint presentation uses wave files and MIDI files (. wav files and. mid files).
• All popular sound file formats, including MP3, WAV, FLAC, MIDI, and WMA, are supported by PowerPoint.
• The IBM and Microsoft-developed Waveform Audio File Format (WAVE, or WAV due to its filename extension; pronounced "wave") is a standard audio file format for storing an audio bitstream on PCs.
• The Musical Instrument Digital Interface (MIDI) standard was created for digital music synthesizers and is used to transmit and store music. Recorded sounds cannot be transmitted using MIDI.

Additional Information GIF Files:- Graphics Interchange Format is referred to as GIF. GIF is a raster file format made for simple graphics that are primarily found online.

JPEG Files:- Joint Photographic Experts Group is referred to as JPEG. One of the most popular image file formats in use today is the JPEG format.

The  correct option is (1)= A1 + A2

Key Points

• In a spreadsheet, the right formula to add two values in cells A1 and A2 are =A1+A2. The SUM function in a spreadsheet is in charge of adding values.
• This means that the selected cell will contain the same value as the outcome of the specified calculation. When you click in a cell and type =A1+A2, for instance, the value of the cell you selected will be equal to the sum of the values in cells A1 and A2.
• To total the numbers, choose a cell next to them, choose AutoSum from the Home menu, and then press Enter. Excel automatically enters a formula (using the SUM function) to sum the numbers when you click AutoSum.

Additional Information

• The Functions Library in Excel has over 475 formulas, ranging from basic mathematical operations to extremely difficult statistical, logical, and engineering tasks like IF statements (one of our all-time favorite tales); AND, OR, NOT functions; COUNT, AVERAGE, and MIN/MAX.
• To perform mathematical computations, an Excel formula is utilised. The equal sign (=) and your calculation are always typed in the cell at the beginning of a formula. Calculations can be performed using formulas like =1+1 and =2*2.

The correct answer is Italic.

Key Points

• Ctrl + I is used to apply the italic format to the selected text. Hence, Option 3 is correct.

Additional Information

• List of Computer Shortcut Keys

To remove unwanted actions from a recorded macro without recording the whole macro again, you can follow these steps:
Step 1: Open the Visual Basic Editor
- Press Alt + F11 to open the Visual Basic Editor.
Step 2: Locate and Select the Macro
- In the Visual Basic Editor, locate the macro that contains the unwanted action.
- Select the macro by clicking on its name in the Project Explorer window.
Step 3: Edit the Macro Code
- Once the macro is selected, the code corresponding to the macro will be displayed in the Code window.
- Scroll through the code to find the unwanted action that you want to remove.
Step 4: Remove the Unwanted Action
- Place your cursor on the line of code that represents the unwanted action.
- Press the Delete key to remove the line of code.
- Repeat this process for any other unwanted actions that you want to remove.
Step 5: Save and Close the Visual Basic Editor
- After removing the unwanted actions, save the changes by clicking on the Save button or pressing Ctrl + S.
- Close the Visual Basic Editor by clicking on the Close button or pressing Alt + Q.
The unwanted actions have now been removed from the recorded macro without having to re-record the entire macro.

The correct answer is Bookmark.

• A Chrome Internet browser, a method of saving web page addresses for quick access is Bookmark.

Key Points

• Bookmark
  • “Bookmark” refers to links to sites that we store for easy access later.
  • A bookmark is a saved shortcut that directs your browser to a specific webpage.
  • It stores the title, URL, and favicon of the corresponding page.
  • Saving bookmarks allows you to easily access your favourite locations on the Web.

Additional Information

• Proxy Setting
  • ​A proxy server acts as a gateway between you and the internet.
  • It’s an intermediary server separating end users from the websites they browse.
• Clear Cache
  • When we use a browser it saves some information from websites in its cache and cookies.
  • Clearing them fixes certain problems, like loading or formatting issues on sites.
• Delete history
  • Windows short cut to delete history:
    • CTRL+SHIFT+DEL

The pattern followed here is:

Hence, the correct answer is "L".

As Peacock is the national bird of India, similarly Bear is the national animal of Russia.

Given:

The side of the square = 22 cm

Formula used:

The perimeter of the square = 4 × a    (Where a = Side of the square)

The circumference of the circle = 2 × π × r     (Where r = The radius of the circle)

Calculation:

Let us assume the radius of the circle be r

⇒ The perimeter of the square = 4 × 22 = 88 cm

⇒ The circumference of the circle = 2 × π ×  r

⇒ 88 = 2 × (22/7) × r

⇒ 

⇒ r = 14 cm

∴ The required result will be 14 cm.

Checking → statement I:

References:

Point A is 3km north of library.

Point C is 3km North of Point B.

Point D is 3km East of point C.

Inferences:

From the above references, we can conclude that instruction about college is missing in statement I.

So, we can’t determine the direction between library and college.

Thus, statement I alone is not sufficient to answer the question

Checking → Statement II:

References:

College is 7km North of point F.

Point D is 6km North of point E.

Library is 7km west of point E.

Point F is 4km East of point E.

Inferences:

From the above references, we can conclude the following.

We can conclude that library is to the South West direction with respect to college.

Thus, statement II alone is sufficient to answer the question.

Hence, option B is correct.

Given:

x + y + 1 = 0

Concept Used:

(a + b )³ = a³ + b³ + 3ab (a + b)

Calculations:

x + y + 1 = 0

⇒ x + y = -1

Cubing on both sides we get

(x + y)³ = ( -1 )³

⇒ x³ + y³ + 3xy( x + y ) = -1

⇒ x³ + y³ + 3xy ( -1) = -1

∵ x + y = -1

⇒ x³ + y³ - 3xy = -1

∴ required value = -1