BEL Trainee Engineer Electronics Mock Test - 8 - Electronics and Communication Engineering (ECE) MCQ

Control system:

A Control system is defined as a device that manages, commands direct, or regulates the behavior of other devices or systems to achieve the desired result.

It is also defined as A system with a provision for controlling the response.

There are two types of control systems.

Open-loop control system:

The open-loop control system can be described by a block diagram as shown in the figure below.

These are the systems in which the control action is independent of output.

Ex: Traffic signals, washing machine and bread toaster, systems having no sensor, etc.

Advantages:

• Simple construction and design
• Cost is less
• Maintenance is easy
• No problem of instability
• Convenient to measure when the output is difficult to measure

Disadvantages:

• These are less accurate, and their accuracy depends on the calibration.
• Inaccurate results are obtained with parameter variations within the system.
• Recalibration of the controller is required from time to time to maintain accuracy.

Closed-loop control system:

The open-loop control system can be described by a block diagram as shown in the figure below.

These are the systems in which the control action depends on the output. These systems have a tendency to oscillate.

Ex: Temperature controllers, speed control of the motor, systems having sensors, etc.

Advantages:

• More accurate
• Non-linear distortions are less
• Output is less sensitive to parameter changes within the system
• Bandwidth increases

Disadvantages:

• Design is complicated
• More expensive
• May become unstable, if there are malfunctions in the feedback.

In position control systems, the device is used for providing rate feedback voltage is called tachogenerator.

PCM is a technique by which an analog signal gets converted into digital form to have signal transmission through a digital network.

The major steps involved in PCM is sampling, quantizing, and encoding.

Low Pass Filter:ccc

• Here, the message signal which is the continuous-time form is allowed to pass through a low pass filter (LPF).
• This LPF whose cutoff frequency is fm eliminates the high-frequency components of the signal and passes only the frequency components that lie below fm.

Sampler:

• The output of the LPF is then fed to a sampler where the analog input signal is sampled at regular intervals.
• This sampling frequency is so selected that it must follow the sampling theorem that is expressed as:

          

• The output of the sampler is a signal that is discrete-time continuous amplitude signal denoted as nTs which is nothing but a PAM signal.

Quantizer:

• A quantizer is a unit that rounds off each sample to the nearest discrete level.
• The Sampler provides a continuous range signal and hence still an analog one.
• The quantizer performs the approximation of each sample thus assigning it a particular discrete level.

Encoder:

• An encoder performs the conversion of the quantized signal into binary codes.
• This unit generates a digitally encoded signal which is a sequence of binary pulses that acts as the modulated output.
• At it is a binary encoder thus generates a binary code sequence. That is transmitted through the transmission path.

Comparator is not used in pulse code modulation.

• The mobility of electrons, which are carriers in the case of an n-channel device, is greater than that of holes, which are the carriers in the p-channel device.
• Thus an n-channel device is faster than a p-channel device.
• The N-channel transistor has lower on-resistance and gate capacitance for the same die area.

1) Handoff operation involves identifying a new base station

2) It also requires that the voice and control signal be allocated to channels associated with the new base station.

3) The dwell time describes the amount of time a mobile spends in a radio cell.

4) The dwell time depends on various parameters like velocity of the user, cell size, cell shape and the traversed path.

The correct answer is 

Key Points

• Given two point charges exert a force F when placed r apart in constant K, the force between them is the same. We have to find R.
• let q₁ and q₂ be two point charges.
• 1/4πE₀q₁*q₂/r2 = 1/4πE₀q₁*q₂/K*R² (where E0= permittivity of air and K = dielectric constant)
• 1/r² = 1/K*R²
• R= 

Lissajous pattern

• When two sinusoidal signals of the same frequency and magnitude are applied to the CRO, the pattern of figures is formed. These figures are Lissajous patterns.
• The shape of these figures depends upon the phase difference of the applied two input signals.
• If the phase difference between the two signals is 0°, then the Lissajous pattern will be a straight line with a major axis in the 1^st and 3^rd quadrants.
• If the phase difference between the two signals is 90° and 270°, then the Lissajous pattern will be a circle.
• If the phase difference between the two signals is 180°, then the Lissajous pattern will be a straight line with a major axis in the 2^nd and 4^th quadrants.

In TV Transmission the use of FM is made for Audio transmission and AM for Video transmission.

Vestigial Sideband Modulation (VSB) is used for video modulation in TV transmission due to the following reasons :

• Video signal exhibits a large bandwidth and significant low-frequency content which suggests the use of VSB.  
• VSB (vestigial sideband) transmission transmits one sideband fully and the other sideband partially thus, reducing the bandwidth requirement.
• The circuitry for demodulation in the receiver should be simple and therefore cheap. VSB demodulation uses simple envelope detection.

The spectrum of a vestigial sideband is as shown:

Ideal Inductor & Capacitor power Dissipation is always 'zero'.

AC through Pure Inductor:

Consider a pure inductor of inductance L connected to an alternating voltage given by,

v = V_m sin ωt

An alternating current (i) flows through the inductor and sets up a changing magnetic field and it induced a back EMF (-L di/dt).

By using KVL,

Integrating on both side,

i = 

or, 

The phasor diagram can be drawn as,

From the phasor diagram, it is clear that the phase angle between voltage and current is 90°.

We know that the power factor is the cosine angle of voltage and current,

Hence, Power Factor = cos ϕ = cos 90° = 0

We know that,

Power Dissipation (P) = VIcos ϕ

Since, ϕ = 90° ⇒ cos ϕ = cos 90° = 0

Hence, Power Dissipation (P) = 0

Content: 

Mobile telephony is the most common mode of communication these days. A mobile phone is like a handy computer equipped with the internet. It has greatly changed our lives. The operation frequency range of telephone is Ultra High-Frequency range. The frequency of outgoing signals and incoming signals is not the same. This prevents intermixing of signals and makes simultaneous communication possible. It works both as a transmitter as well as a receiver which can both send and receive signals in the radio frequency range. 

The most common applications of mobile telephony are-

• Receiving and sending signals (calling facility)
• Taking photos and videos
• Sending text messages
• Playing games
• receiving e-mails
• Listening to music and so on.

Explanation:

A mobile phone is low powered transceiver i.e., a combination of both transmitter and receiver. It can wirelessly send and receive signals.

The correct answer is option (3)

An active filter is a type of analog circuit implementing an electronic filter using active components, typically an amplifier. Amplifiers included in a filter design can be used to improve the cost, performance and predictability of a filter.

Types of active filters. 

• Butterworth 
• Chebyshev 
• Bessel
• Elliptic filters.

Butterworth Filter:

• This filter is also called as maximally flat or flat flat filter. This class of filters approximates the ideal filtted in the pass band. 
• The Butterworth filter has an essentially flat amplitude-fre­quency response upto the cut­off frequency. 
• Butterworth filters has the sharpest attenuation, their phase-shift as a function of frequency is non-linear.
• It has a monotonic drop in gain with frequency in the cut-off region and a maximally flat response below cut-off frequency.
• The Butterworth filter has characteristic somewhere be­tween those of Chebyshev and Bessel filters.
• It has a moderate roll-off of the skirt and a slightly non­linear phase responses.

Chebyshev Filter:

• It is also called a equal rip­ple filter.
• It gives a sharper cut-off than Butterworth filter in the passband.
• Both Butterworth and Chebyshev filters exhibit large phase shifts near the cut-off frequency.
• A drawback of the Chebyshev fil­ter is the appearance of gain maxima and minima below the cut-off frequency.
• This gain ripple, ex­pressed in db, is an adjustable parameter in filter design.
• A Chebyshev filter is used where very sharp roll-off is required. However, this is achieved at the expense of a gain ripple in the lower frequency passband.

Bessel Filter:

• The Bessel filter provides ideal phase characteristics with an approximately linear phase re­sponse upto nearly cut-off frequency.
• Though it has a very linear phase response but a fairly gentle skirt slope.
• For applications where the phase characteristic is important, the Bessel filter is used.
• It is a minimal phase shift filter even though its cut-off characteristics are not very sharp.
• It is well suited for pulse applica­tions.

Elliptic Filter:

• This filter has the sharpest roll-off of all filters in the transition region but has ripples in both the pass band and stop band regions.
• The elliptic filter can be designed to have very high attenuation for certain frequencies in the stop band, which reduces the attenuation for other frequencies in the stop band.

Layer 2 Ethernet Frame Format:

MAC address consists of 6 bytes

1 byte = 8 bits

∴ 6 bytes = 6 × 8 bits = 48 bits

MAC address has 48 bit or 6 bytes

Concept:

Calculation:

Concept:

Let, s = No of error that can be detected

t = No of error that can be corrected

dmin = Minimum hamming distance for the code

Then,

To detect up to 's' errors

1) dmin ≥ s + 1

To correct up to 't' errors

2) dmin ≥ 2t + 1

it can detect up to 's' errors and correct up to 't' errors if and only if:

3) dmin ≥ t + s + 1

Calculations:

Given:

Error detected = 2 = s

Error corrected = 1 = t

From(1),

dmin ≥ 3

From(2),

dmin ≥ 3

We need to find for both correction and detection and hence, 

Using formula (3)

dmin ≥ t + s + 1

dmin ≥ 2 + 1 + 1

dmin = 4

PMMC instruments:

• The scale is uniform (Linear scale)
• High torque to weight ratio compared to all the other type of instruments
• Frequency error or reactance error is absent
• High sensitivity
• Hysteresis loss is lesser
• No internal heating problem
• High accuracy
• Very less power consumption

Important Points

Moving Iron (MI) type instruments:

• Moving Iron (MI) type instruments can be used for both AC & DC measurements. But Moving Iron connected through the current Transformer block DC supply. So that Moving Iron connected through the current Transformer is only used for AC measurements.
• The moving iron meter has a large magnetic reluctance as compared to the PMMC meter. That’s why more power is required to operate the moving iron meter.

Additional Information
Comparison of Moving Coil, Dynamometer type and Moving  Iron Voltmeters and Ammeters:

Explanation:

Any laplace domain function into z-domain we need a conversion.

z-transform: Any discrete sample in z-domain.

Laplace transform: Any continuous time signal into lapalce domain.

For conversion we take e^sT = z

taking log on both sides

ln (e^sT) = ln z

sT = ln z

s = (ln z)/T

DC ampere-hour meter

• DC ampere-hour meter works on the chemical effect of current.
• It is used to calculate the amount of electricity charge used by multiplying the flow rate of electrons by the number of times electrons flow through the wire.
• The principle of working of all electrical measuring instruments depends upon various effects of electric current or voltage as shown in the table given below:

Immediate addressing mode:

It is the simplest form of addressing mode, in which the operand value is present in the instruction. This mode is used to define and use constants or set initial values of variable. In this, no memory reference other than the instruction fetch is required to obtain the operand.

Implied addressing mode:

In this, operands are specified in the definition of instruction. It is used for zero address instructions.

Register addressing mode:

In register addressing mode, the address field refers to a register rather than a main memory address. In this, only a small address field is needed in the instruction and no time-consuming memory references are required.

Index addressing mode:

In this, operand is the address that is sum of index register and displacement. It needs memory reference.

It is not, therefore with any feeling of unfriendliness to a particular member of that class that I pay tribute to conductors as a class.

One meaning of fathom is to comprehend, and hence misconstrue is the closest antonym.

The correct answer is option 3, i.e. = (equal sign).

All the formulas in MS Excel started with an equal sign.

• After equal sign one can add formula or function.
• For example, the addition of values in cells A1 through A4, then type the whole equation after the equal sign.
  • = A1 + A2 + A3 + A4.
• The ampersand operator (&) joins several strings into one string.
• The dollar sign ($) is used for creating absolute references.

The correct answer is Ctrl + c, Ctrl + v.

Important Points

Ctrl + c is used to copy text and Ctrl + v is used to paste it.

Additional Information

Some other shortcuts-

•  Ctrl+Z- undo
•  Ctrl+X- Cut
•  Ctrl+F- Find
•  Ctrl+P- Print

The correct answer is Magnetic Ink Character Recognition.

Key Points

• Magnetic ink character recognition is abbreviated as MICR.
• Magnetic ink character recognition (MICR) is a check identification and processing method.
• The MICR on a check is the string of characters at the bottom left corner of the check.
• The bank routing number, the account number, and the check number are among the three groupings of numbers.
• MICR numbers are intended to be read by both humans and sorting machines.
• Due to the usage of magnetic ink and unique fonts, they can't be faked or replicated.
• Enhanced protection against fraud and mechanisation of check processing are two of the technology's advantages.
• MICR was created in the late 1950s and is currently used all over the world.

To change the column width to fit the contents in a spreadsheet, you can follow these steps:
1. Double click the boundary to the right of the column heading:
- Position your cursor on the boundary between the column heading and the next column to the right.
- The cursor will change to a double-sided arrow.
- Double click the boundary to automatically adjust the column width to fit the contents of the column.
2. Alternative methods:
- Single-click the boundary to the left of the column heading and drag it to manually adjust the column width.
- Right-click the column heading and select "Column Width" from the context menu. Enter a specific width value or choose "AutoFit" to adjust the width based on the content.
3. Keyboard shortcuts:
- Press and hold the "Alt" key and single-click anywhere in the column to automatically adjust the width to fit the contents.
- Alternatively, you can select the column by clicking the column heading and then press "Alt + O + C + A" to automatically adjust the width.
Remember, adjusting the column width to fit the contents can help optimize the appearance and readability of your spreadsheet.

Spreadsheet program
A spreadsheet program is a computer program that organizes data in rows and columns of cells. It is commonly used to perform calculations, analyze data, and create charts or graphs. In the context of keeping a record of the money earned from mowing lawns over the summer, a spreadsheet program would be the most suitable choice. Here's why:
- Organizes data in rows and columns: A spreadsheet program allows you to input and organize data in a tabular format, with rows representing individual records and columns representing different attributes or variables. This structure is ideal for keeping track of earnings, dates, and other relevant information related to lawn mowing jobs.
- Performs calculations: Spreadsheet programs have built-in formula functions that enable you to perform calculations and manipulate data. For example, you can easily calculate the total earnings for the summer by summing up the amounts from the respective cells.
- Provides data analysis tools: With a spreadsheet program, you can analyze your earnings data by using functions like averages, sorting, filtering, and creating charts or graphs. This allows you to gain insights and visualize trends or patterns in your lawn mowing business.
- User-friendly interface: Spreadsheet programs typically have a user-friendly interface that allows you to easily input, edit, and navigate through data. You can format cells, apply conditional formatting, and customize the appearance of your spreadsheet to make it more visually appealing and organized.
- Data storage and retrieval: Spreadsheet programs provide a convenient way to store and retrieve data. You can save your spreadsheet as a file on your computer or in the cloud, ensuring that your records are easily accessible and can be updated as needed.
In conclusion, a spreadsheet program is the most suitable choice for organizing and managing the data related to your lawn mowing earnings. It offers the necessary features and functionality for efficient record-keeping, calculations, analysis, and data storage.

Hence, option A is correct.

From the common explanation, we get Sona sits opposite Bobby.

Hence, Option E is correct.

Final Arrangement:

Common Explanation:

References:

Eight students Kirti, Ayushi, Manu, Sona, Aarti, Bobby, Ankita and Divya are sitting around the square table.

Four students sit on each side while rest on each corner.

Students at the side face away from the centre and students at the corner faces towards the centre.

Inferences:

So, we need to arrange as follows to accommodate the information as stated in the question,

References:

Divya sits third to the left of Ayushi.

Kirti sits opposite to Manu and both faces away from the centre.

Inferences:

From the above references, we get the following two different cases:

Case 1:

Case 2:

References:

Neither Kirti nor Manu are beside Ayushi.

Sona sits immediate left of Ankita, who sits on the side of the table.

Bobby is not an immediate right of Ayushi.

Bobby is not adjacent to Manu.

Inferences:

So, from this case 2 will be eliminated as neither Kirti nor Manu are beside Ayushi.

Now, from case 1 we get the following final arrangements:

As 'Grease' is prepared from 'Wax' in the same way 'Curd' is prepared from 'Milk'.

As the cry of 'Dog' is called 'Bark' in the same way the cry of 'Goat' is called 'Bleat'.