Physical Layer in the OSI Model: It’s Functions, component and Protocols.

7-layer-of-osi-model

Physical Layer in the OSI Model: Functions, component and Protocols

In an OSI (Open Systems Intercommunication) model, the physical layer (Layer 1) is the lowest or bottom most layers of OSI model, which standardizes the functions of a telecommunication or computing system. The primary responsibility of the Physical Layer is to transmit raw bitstreams coming from upper layer (Data link layer) over a physical medium. Physical layer establishes, maintains and deactivates the physical connection.

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What Is computer Network?

Data rate also maintained by the function of the Physical Layer. It defines how two or more devices are connected to a link by line configuration. Physical layer also maintain the Synchronization between sender and receiver. This layer also provide functionality to its upper layer called Data Link Layer (DLL). Physical layer pick data from data link layer and encode it at the sender side and decode data at the receiver side.

Physical layer In OSI model

Physical Layer in the OSI Model: Its Functions

Physical Layer in the OSI Model

Functions of the Physical Layer

The key responsibility of physical layer is sending bits from one node to another node along the network. Its role is determining how physical connections to the network are set up, as well as how bits are represented into signals — as they are transmitted either in the form of electrical signal, optical signal or by radio waves.

To do all this, the physical layer performs a different functions, that are given below:

  1. Bit Transmission: The Physical Layer is responsible for transmitting raw bits (0s and 1s) from one node to another over a physical medium, such as cables, fiber optics, or radio waves.
  2. Signal Encoding: It converts the data bits into signals that can be transmitted over the physical medium. This include encoding bits into electrical, optical, or radio signals depending on the medium used.
  3. Data Rate Control: It determines the rate at which data is transmitted over a physical medium, which is usually measured in bits per second (bps). This data rate can vary depending on the transmission medium and the technologies used.
  4. Topologies: It defines how two or more devices physically and logically connect to make a network. There are six types of topologies such as bus topology, star topology, ring topology, and mesh topology, tree topology and hybrid topologies.

5. Transmission Modes: It describes the direction of the data flow. Transmission modes are classified into three types: Simplex, Half-Duplex, and Full-Duplex.

6. Interfaces and Standards: The Physical Layer defines the hardware specifications and interfaces, including pin layouts, voltage levels, cable types, connectors, and other physical attributes. Examples include RS-232, RJ45, and V.35.

7. Multiplexing: Multiplexing is the process of combining multiple data streams and send it through a single stream for transmission over a communication channel.  It uses different methods like Frequency Division Multiplexing (FDM) or Time Division Multiplexing (TDM) to allow multiple signals to share the same physical medium. Multiplexing is done at the sender side and demultiplexing is done at receiver side.

Components of the Physical Layer

  1. Cables and Connectors: Physical layer use physical media such as twisted pair cables, coaxial cables, optical fiber cables, and wireless media (radio waves, microwaves).
  2. Network Interface Cards (NICs): It is a hardware device that connects a computer to a network.
  3. Repeaters and Hubs: These are the devices that is use to extend the range of a network by amplifying the signals.
  4. Modems: It is a devices that modulate and demodulate signals for transmission over telephone lines or cable systems.

Physical layer Standards and Protocols

  1. Ethernet (IEEE 802.3): It specifies the physical and data link layer’s operation in wired Ethernet networks.
  2. Wi-Fi (IEEE 802.11 ): It governs wireless networking.
  3. Optical Transport Network (ITU-T G.709): it defines the standard for optical fiber networks.
  4. SONET/SDH: It is a standards for synchronous optical networking.

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Examples of physical layer technologies

  1. Ethernet: The most widely used LAN technology that operates at both the data link and physical layers. Uses various media like twisted pair (Cat5e, Cat6) and fiber optics.
  2. Fiber Optics: It uses light signals for high-speed data transmission over long distances with minimal loss.
  3. DSL (Digital Subscriber Line): It uses existing telephone lines to provide high-speed internet access.
  4. Wi-Fi: Wireless technology that provides high-speed internet and network connections.

What is the Physical Layer in the OSI Model?

The Physical Layer is the first and lowest layer of the OSI (Open Systems Interconnection) model. It is responsible for the transmission and reception of raw bit streams over a physical medium, such as cables, optical fibers, or radio waves.

What are the main functions of the Physical Layer?

1. Bit Transmission: Transmits raw bits from one device to another.
2. Signal Encoding: Converts bits into signals suitable for the transmission medium.
3. Data Rate Control: Manages the speed at which data is transmitted.
4. Physical Topologies: Defines the physical layout of network devices.
5. Transmission Modes: Supports simplex, half-duplex, and full-duplex modes.
6. Synchronization: Ensures sender and receiver are synchronized.
7. Multiplexing: Allows multiple signals to share the same medium.
8. Physical Interfaces and Standards: Specifies hardware details like pin layouts and voltage levels.

What are some common physical media used in the Physical Layer?

1. Twisted Pair Cables: Commonly used for Ethernet connections.
2. Coaxial Cables: Used for cable TV and internet.
3. Fiber Optic Cables: Provides high-speed data transmission over long distances.
4. Radio Waves: Used for wireless communications like Wi-Fi and Bluetooth.

What are some devices associated with the Physical Layer?

1. Network Interface Cards (NICs): Connect computers to networks.
2. Repeaters: Amplify signals to extend the range of a network.
3. Hubs: Basic devices that connect multiple Ethernet devices.
4Modems: Modulate and demodulate signals for transmission over telephone lines or cable systems.

Quantization and its Types

Looking for what is Quantization and its types?

In this article, we explained all the important points regarding quantization in detail.

let’s understand the topic:

Quantization is a process of converting discrete time continuous valued signal (discrete time signal) into discrete time discrete valued signal (digital signal). Other definition of quantization, It is the process of mapping the infinite range of continuous values signal to a finite set of discrete values signal or levels.

The device that performs quantization is called Quantizer. Quantifying an continuous analog signal is done by discretizing the signal with a number of quantization levels.

In quantization, the amplitude of sampled signal is round off to the nearest quantized level. This rounding off is known as quantization error. By increasing the numbers of quantization levels we can reduce the quantization error.

Quantization of an Analog Signal

Quantization is a process of ” Rounding off the sampled value to the nearest quantization level”.

Here I explain the step-by-step quantization process of an continuous analog signal.

Steps of quantization

  1. Divide the sampled signal amplitude (voltage range) into L different level.
  2. The number of level or value of L is depend upon “number of bit that encoder can encode” L is given by L= 2n where n is the
  3. The number of level or value of L is depend upon “number of bit that encoder can encode” L is given by L= 2n where n is the number of bit that encoder can encode. If we have 4-bit encoder it means the value of n=4 so we divide the signal amplitude into L=24=8 level.
  4. If the number of level is more the quantization error is less and vice-versa.
  5. The space between two interval is called step size (Δ or S). Step-size (Δ or S )= VH-VL / L where VH is max and VL is lowest value of sampled voltage.
  6. Now, draw mid line at S/2, representing quantization levels.
  7. Now, assign binary codes to each quantization level.

8. Now, calculate the quantization error, which is the difference between the original sampled value and the quantized value. This error represents the loss of information due to quantization.

The figure given below shows how an continuous analog signal gets quantized. Here, the blue line represents continuous analog signal and the brown one represents the quantized signal.

This figure shows the resultant quantized signal which is the digital form for the given analog signal.

This is also called as Stair-case waveform, in accordance with its shape.

Types of Quantization

There are basically two type of quantization

Delta Modulation (∆-modulation)-Digital Communication

Looking for delta modulation (DM or ∆-modulation)?

In this article we explained all main and important points regarding Delta Modulation (DM) in detail.

let’s understand the topic:

like PCM (Pulse Code Modulation) and DPCM (Differential Pulse Code Modulation), Delta modulation (DM or Δ-modulation) is also a analog-to-digital modulation technique used for converting analog signals into digital format. It’s particularly suitable for signals with relatively slow variations.

In PCM , N-number of bit are transmitted per sample. Therefore, bandwidth requirement is very large. To overcome this problem we use delta modulation. In this scheme, only 1 bit is used to encode 1 voltage level thus, the technique allows to transmission only one bit per sample.

Read more: DPCM (Differential Pulse Code Modulation)

PCM (Pulse Code Modulation)

Sampling Theorem

Characteristics of delta modulation

It reduces the delivered data to a 1-bit data stream. It has the following characteristics:

  1. It is a simplified form of DPCM technique also known as 1-bit DPCM scheme.
  2. Here two sample values are compared, and result of this comparison is transmitted.
  3. Here input sequence is much higher than the Nyquist rate.
  4. It is simple to implement in both hardware and software compare other modulation scheme.
  5. Here quantization is simple, encoded signals which are over-sampled.
  6. Here, step-size is very small and fixed, i.e. Δ delta.
  7.  It provides a staircase approximation of over-sampled base-band signal.
  8. Here bit rate can be decided by the user.

Operating Principle of delta modulation

In delta modulation, present sample value X(nTs) is compared with previous approximated sampled value  x^(nTs), and the result of this comparison is encoded and transmitted.

The compared value is called delta (Δ) value. The delta value is then compared to a predefined threshold or step size.

If present sample value X(nTs) is greater than previous approximated sampled value  x^(nTs) then the step of the signal denoted by Δ is increased by 1.  If present sample value X(nTs) is smaller than previous approximated sampled value  x^(nTs) then step of the signal is decreased by 1 i.e., reduction in Δ.

mathematically,

X(nTs) > x^(nTs) +Δ i.e., increase in step size, then 1 is transmitted.

X(nTs) < x^(nTs) –Δ i.e., decrease in step size, 0 is transmitted.

Hence, delta modulation transmitted only one bit per sample.

Delta Modulation

Block Diagram of Delta Modulation

Let’s understand first the generation and detection of delta modulated signal.

Generation of delta modulated signal

The block diagram given bellow shows the generation of delta modulated signal:

Delta Modulator consist of a 1-bit quantizer and a delay circuit along with two comparator circuits.

Block diagram of delta modulation

The sampled signal x(nTs) and previous approximated sampled value  x^(nTs) generated by accumulator circuit, is given to comparator circuit. The output of comparator circuit is an error signal ep(nTs) given by.

ep(nTs)=x(nTs)−xˆ(nTs)

This error signal ep(nTs) is given to the quantizer circuit. The quantizer quantizes the error signal ep(nTs). The quantizer generates the output in the form of steps. If positive magnitude pulse is provided to the quantizer as its input then quantizer performs increment by 1 step size, Δ.

It means that positive pulse at the output of the comparator circuit shows that message signal is greater than the arbitrary signal. Thus quantizer increases Δ by 1.

Similarly, If negative magnitude pulse is provided to the quantizer as its input then quantizer performs decrement by 1 step size, Δ. Thus, quantizer decreases Δ by 1.

The output of the quantizer at the same time, through a feedback path, is provided to the accumulator. An accumulator is nothing but a device that stores the signal for further operation. Thus, output of the accumulator is behaves like the second input of the comparator. 

Finally,  depending on the staircase signal if the step size is +Δ then binary 1 is transmitted and if it is –Δ then binary 0 is transmitted.

Detection of delta modulated signal

Detection of a delta modulated signal is very easy and is somewhat reverse of generation of a delta modulated signal.

It is a process of decoding the binary output of the delta modulator to reconstruct an approximation of the original analog signal. The goal is to reverse the encoding process and recover an estimate of the continuous analog signal from the binary data.

The block diagram given bellow shows the detection of delta modulated signal:

It consist of a accumulator circuit and LPF (low pass filter).

The accumulator consists of a comparator circuit and a delay unit. The transmitted signal along with the delayed signal is added at the comparator circuit.

If here the input is binary 1 then after a delay the output increased step size +Δ noticed. However, in the case of binary 0 as input, a decrease in step size is noticed. This generates the staircase signal equivalent to the message signal.

The output of the accumulator circuit is given to the LPF that smoothens the staircase signal to regenerate the original message signal.

Advantages of delta modulation

  1. It is relatively simple to implement.
  2. It has less components and computational requirements compared to Pulse Code Modulation (PCM).
  3. It has lower bit rate compared to PCM.
  4. It is particularly useful in telecommunications.
  5. It is well-suited for real-time applications, such as audio and video streaming.
  6. It permits low channel bandwidth as well as signaling rate due to transmission of 1 bit per sample.

Disadvantages of delta modulation

The main disadvantages of DM are

  1. Slope Over load distortion [occur when step size (Δ) is small]
  2. Granular noise [occur when step size (Δ) is large]

What is delta modulation?

Delta modulation is a digital modulation technique used to convert analog signals into digital format by encoding the difference (delta) between consecutive samples of the analog signal.

What is the purpose of delta modulation?

The main purpose of delta modulation is to efficiently represent analog signals with low bit rates, making it suitable for applications with limited bandwidth or storage capacity.

Read more: wiki

Differential Pulse Code Modulation (DPCM)

Looking for Differential Pulse Code Modulation (DPCM)?

In this article we explained all main and important points regarding Differential Pulse Code Modulation (DPCM) in detail.

let’s understand the topic:

 In PCM (Pulse code modulation) It is observed that, the adjacent samples of a signal are highly correlated with each other. So, the adjacent sampled valued signal does not much change.  Which means , present sampled value to next sampled value does not vary by a large amount. It means, the adjacent samples of the signal carry the same information with a small difference. 

Read more: Pulse Code Modulation (PCM)

Sampling Theorem

The adjacent samples of the signal carry lots of redundant information. If these samples are encoded by a Standard PCM system, the resulting encoded signal contains some redundant bits (redundant information).

Figure 1 below shows a continuous time signal x(t) by dotted line. This signal is sampled by flat top sampling at regular time intervals T, 2T, 3T …..  nTs .

Figure 1: Redundant Information in PCM (Pulse code modulation)

Here, sampling frequency is selected in such a way, it is higher than the Nyquist rate. These samples are encoded by using 3-bit (7 levels) PCM. In figure 1, small circles shown the quantized value of samples to the nearest digital level. On the top of the each samples encoded binary value is written. Here we see in figure 1, that the samples taken at 4T, 5T and 6Tare encoded to same value of (110). This information can be carried only by one sample value. But three samples are carrying the same information means redundant.

Now, consider another example of samples taken at 9Ts and 10Ts time interval. The difference between these samples only due to last bit and first two bits are redundant, since they do not change. If this redundancy is reduced, then overall bit rate will decrease and number of bits required to transmit one sample will also be reduced. This is obtained by a digital pulse modulation technique is called as Differential PCM (DPCM) technique.

Working Principle of Differential pulse code modulation (DPCM)

DPCM works on the principle of prediction. The present sampled value is predicted from the past sampled value. The predicted value may not be exact, but it is very near to the actual sampled value.

Working of DPCM is explained with the help of block diagram of DPCM transmitter section and DPCM receiver section.

Differential pulse code modulation (DPCM) Transmitter

Figure 2 given below shows the block diagram of DPCM transmitter section.

Figure 2: Block DPCM transmitter section

The main components of DPCM transmitter are comparator, quantizer, prediction filter, and an encoder.

Let x(t) be the signal to be sampled and x(nTs) be its samples. The predicted signal is indicated by x^(nTs). Now x(nTs) sampled signal and x^(nTs) predicted signal is given to the comparator. The comparator in the transmitter, finds out the difference between the actual sample value x(nTs) and predicted sample value xˆ(nTs). The output of comparator is called error signal and it is denoted by e(nTs).

The output of comparator is given by,

e(nTs) = x(nTs) – xˆ(nTs)……………………….(1)

The predicted sample value xˆ(nTs) is produced by using a prediction filter.

Now, the output of comparator e(nTs) is given to the quantizer.

Quantizer output,

eq(nTs) = Q[e(nTs)] = e(nTs) + q(nTs) ……………………..(2)

The quantizer output signal eq(nTs) is called quantized error signal eq(nTs).

By encoding the quantizer output, in this method, we obtain a modified version of the PCM called differential pulse code modulation (DPCM).

Now, to makes the prediction more and more close to the actual sampled signal. The quantizer error signal eq(nTs) and the previous prediction is added and given as input to the prediction filter, this signal is denoted by xq(nTs). 

Predictor input is the sum of quantizer output eq(nTs) and predictor output xˆ(nTs)

xq(nTs) = xˆ(nTs) +  eq(nTs)……………………..(3)

 Now, put the value of  eq(nTs) from eq.(2)  in the above eq. (3) , we get,

xq(nTs) = xˆ(nTs) +  e(nTs) + q(nTs) ………………….(4)

So, the equation (1) is written as,

e(nTs) = x(nTs) – xˆ(nTs)

we get x(nTs) from the above equation

x(nTs) = e(nTs)  +  xˆ(nTs)

by putting the value of  e(nTs)  +  xˆ(nTs) from the above equation into equation 4, we get,

xq(nTs) = x(nTs) + q(nTs) …………………..(5)

From equation (5) we can say that, the input of the predictor xq(nTs) is the sum of original sample value x(nTs) and quantized error q(nTs). 

DPCM receiver

Figure 3 given below shows the block diagram of DPCM receiver section.

The DPCM receiver section consists of a decoder to reconstruct the quantized error signal from incoming DPCM input signal. The decoder output eq(nTs) and predictor output xˆ(nTs) are summed up to give xq(nTs) the quantized version of the original signal. Correspondingly the receive output signal differs from the input x(nts) only by the quantizing error q(nTs).

Figure 3: Block Diagram DPCM Receiver Section

Advantages of Differential pulse code modulation (DPCM)

There are three important advantages of Differential Pulse Code Modulation technique (DPCM) are given below:

  1. Reduced Bitrate: By using DPCM efficiently reduces the bitrate of digital audio signals by encoding the difference between consecutive samples. This means that instead of transmitting or storing each sample individually, DPCM only transmits the changes or variations in the signal, resulting in a lower data rate.
  2. Improved compression efficiency: DPCM reducing redundancy in the signal. It can achieve better compression ratios than PCM, by encoding the difference between two consecutive samples.
  3. Lower quantization noise: DPCM encodes the differences between two consecutive samples, it’s less sensitive to quantization errors than PCM.
  4. Simplicity of implementation: conceptually, DPCM is more simpler than other compression techniques like transform coding (used in JPEG and MP3), making it easier to implement in hardware or software.

Read more wiki

What Is DPCM?

DPCM stands for Differential Pulse Code Modulation. It is a digital signal compression technique that encodes the difference between consecutive samples in a signal or data stream.

How does DPCM differ from PCM?

In Pulse Code Modulation(PCM), each sampled signal is quantized and then encoded independently. But in DPCM, find the difference between the two consecutive sample and encode, It reduces the redundancy.

What is the main advantage of using DPCM?

By using DPCM efficiently reduces the bitrate of digital audio signals by encoding the difference between consecutive samples. This means that instead of transmitting or storing each sample individually, DPCM only transmits the changes or variations in the signal, resulting in a lower data rate.

When is DPCM commonly used?

DPCM is commonly used in telecommunications for voice and video compression, as well as in image and audio compression applications.

Pulse Code Modulation (PCM) – It’s Block Diagram

Pulse code modulation (PCM) is a digital modulation technique by which analog signal gets converted into digital form for transmission, storage, or processing. It involves sampling, quantizing, encoding, and, if needed, reconstructing the original analog signal.

Basics of Pulse Code Modulation (PCM)

Pulse Code Modulation (PCM) is a digital scheme, that digitize all forms of analog data, including video, audio, music, telemetry, etc. In PCM, the continuous analog signal is discretized into discrete values, which are then encoded into binary numbers.

This technique is widely used in various applications, such as telecommunications, audio recording, and data transmission, to convert and transmit analog information in a digital format, It allow efficient storage, transmission, and processing of signals while maintaining a high level of fidelity.

Pulse code modulation (PCM) is a digital modulation technique where as PPM (pulse position modulation), PWM (pulse width modulation) are the example of analog modulation techniques.

Read more: Block Diagram of Digital Communication

2. Sampling Theorem

Block Diagram of PCM

A communication system consist of three section a transmitter, communication channel, and receiver. A transmitter and a receiver have various components depending on the input signal and the output requirements. Transmitter perform modulation and receiver perform demodulation functions. 

In modulation process, sends the message signal with the carrier signal, which helps in enhancing the signals’ characteristics. It also removes any noise, interference, or distortion in the signal. The demodulation process recovers the original signal to make it suitable for the receiver.

Pulse code modulation my youTube video in Hindi

The block diagram of the Pulse Code Modulation (PCM) system is shown below:

1. Transmitter Section: The transmitter section consist of low pass filter, sampler, quantizer, encoder. The function of all the component explained below.

Analog Signal Input: PCM starts with an analog signal as its input. This analog signal can represent various types of data, such as audio waveforms in the case of voice or music.

Block Diagram of Pulse Code Modulation (PCM)

Image credit: tutorialspoint

LPF (low pass filter):Low Pass Filter (LPF) passes all the low frequency and rejects the higher frequencies from the input signal. It is done to avoid the problem of aliasing or distortion in the input signal.

Sampler: Sampling refers to the process of converting continuous time signal into discrete form this is done by sampler.

In this process the continuous time signal (analog signal) is sampled at regular time intervals. Each sample take the instantaneous amplitude of the analog signal at that moment. The rate at which these samples are taken is called the “sampling rate” or “sampling frequency.” According to Nyquist’s theorem, the sampling rate must be at least twice the highest frequency present in the analog signal to avoid aliasing.

The output of sampler is a discrete time signal.

Quantizer: After sampling, each sample’s amplitude is quantized using quantizer. This involves dividing the range of possible amplitudes into a finite number of discrete levels. The number of quantization levels is determined by the “bit depth” or “resolution.” Common bit depths are 8 bits, 16 bits, or 24 bits. More bits allow for finer amplitude resolution.

Encoder: The digitization of analog signal is done by the encoder. Each quantization level is assigned a unique binary code or digital word. The length of this binary code is determined by the bit depth. For example, with 8-bit PCM, there are 256 quantization levels, each represented by an 8-bit binary code.

2.Communication channel: A communication channel is a medium between the transmitter and the receiver. The PCM bitstream can be transmitted over digital communication channels. It also includes a repeater and regenerator that can regenerate the coming digital signal, increase signal strength, and reduce effect of noise.

3. Receiver section: The receiver section consist of decoder, Reconstruction Filter. The function of all the component explained below.

Decoder: Decoder perform the opposite operation of encoder placed in the transmission section. The digitally encoded signal arrives at the receiver. It first removes the noise from the signal. Then decoder circuit decodes the receive pulse coded waveform to reproduce the original signal. This circuit acts as the demodulator.

Reconstruction Filter: To smoothen the reconstructed analog signal and remove high-frequency components introduced during quantization, a reconstruction filter is often used.

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What is PCM, and how does it work?

PCM stands for Pulse Code Modulation. It’s a method of digitally encoding analog signals by sampling the signal’s amplitude at regular intervals, quantizing the samples into binary values, and then encoding them into a digital bitstream.

What is the purpose of sampling in PCM?

Sampling in PCM involves measuring the amplitude of an analog signal at specific time intervals. This process converts the continuous analog signal into discrete data points for digital representation.

What is quantization, and why is it necessary in PCM?

Quantization involves assigning a discrete value (usually binary) to each sampled amplitude. It’s necessary to represent the analog signal accurately in digital form. The number of quantization levels determines the bit depth, which affects the signal’s resolution.

What is the Nyquist Theorem, and how does it relate to PCM?

The Nyquist Theorem states that the sampling rate must be at least twice the highest frequency component in the analog signal to accurately reconstruct it from its samples. PCM adheres to this principle to avoid aliasing.

What are the advantages of using PCM for audio recording?

PCM offers high-fidelity audio representation, compatibility with a wide range of devices and software, robustness against noise, and flexibility in terms of adjusting audio quality.

Top Electrical Measurements and Measuring Instruments MCQ (Multiple Choice Questions)

Here I discuss Top Electrical Measurements and Measuring Instruments MCQ (Multiple Choice Questions)

Q1. which Instruments measure the total quantity of electricity delivered in a particular time. ​
a) Absolute​
b) Indicating​
c) Recording​
d) Integrating​

Answer: Integrating​

Q2. Which of the following are Integrating instruments?​
a) Ammeters​
b) Voltmeters​
c) Wattmeters​
d) Ampere-hour and Watt-hour meters​

Answer: Ampere-hour and Watt-hour meters​

Q3. Resistances can be measured with the help of​
a) Wattmeters​
b) Voltmeters​
c) Ammeters​
d) Ohmmeters and resistance bridges 

Answer: Ohmmeters and resistance bridges 

Q4. Which of the following essential features is possessed by indicating instrument?​
a) Deflecting device​
b) Controlling device​
c) Damping device​
d) All of the above

Answer: Controlling device​

Q5. The household energy meter is​
a) Absolute Instrument​
b) Indicating Instrument​
c) Recording Instrument​
d) Integrating Instrument​

Answer: Integrating Instrument​

Q6. The pointer of the indicating instrument should be​
a) Very light​
b) Very heavy​
c) Very thick and wide​
d) Neither very light nor very heavy​

Answer: Very light

Q7. A moving-coil permanent-magnet instrument can be used as  ……….  by using a low resistance shunt.​
a) Ammeter​
b) Voltmeter​
c) Flux-meter​
d) Ballistic galvanometer

Answer:  ​Ammeter​

Q8. Which of the following properties damping oil must possess?​
a) Must be a good insulator and non-evaporating​
b) Should not have corrosive action upon the metal of the vane​
c) The viscosity of the oil should not change with the temperature​
d) All of the above

Answer:  ​All of the above

Q9. A moving-coil permanent-magnet instrument can be used as flux-meter​
a) By using a low resistance shunt​
b) By using a high series resistance​
c) By eliminating the control springs​
d) By making control springs of large moment of inertia

Answer: By eliminating the control springs​

Q10. An induction meter can handle current upto​
a) 10 A​
b) 30 A​
c) 60 A​
d) 100 A​

Answer: 100A

Q11. Induction type single phase energy meters measure electric energy in​
a) KW​
b) Wh​
c) KWh​
d) VAR​

Answer: KWh

Q12. Which of the following meters are not used on DC circuits?​
a) Mercury motor meters ​
b) Commutator motor meters​
c) Induction meters​
d) None of the above ​

Answer: Induction meters​

Q13. A potentiometer may be used for​
a) Measurement of resistance​
b) Measurement of current​
c) Calibration of ammeter and voltmeter​
d) All of the above ​

Answer: All of the above ​

Q14. Which instrument is used for measuring the insulation resistance of an electric circuit relative to earth and one another?​
a) Tangent galvanometer​
b) Megger​
c) Current transformer​
d) None of the above ​

Answer: Megger​

Q15. Which of the following meters are not used on DC circuits?​
a) Mercury motor meters ​
b) Commutator motor meters​
c) Induction meters​
d) None of the above ​

Answer: Induction meters​

Read More Power Electronics MCQ

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Sampling Theorem | Sampling In PCM | Digital Communication

The sampling theorem, also known as the Nyquist-Shannon sampling theorem, is a fundamental concept in signal processing and digital communication.

Sampling is a process of converting a continuous-time analog signal into discrete-time signal. This conversion is done with the help of sampler.

Sampling is the second step in Pulse Code Modulation (PCM) technique where we convert analog signal into digital signal. In PCM after sampling amplitude of the discrete-time signal is quantized with the help of quantizer and then this quantized signal is coded to the binary sequence using encoder, allow the computer to process the signal, then transmitted to the far end receiver then it is converted back to the original signal.

Read more “Block Diagram of Digital communication”

Need for Sampling

Most of the real-life signals, such as audio, video, temperature etc., are continuous in nature and represented as analog signals. However, for efficient processing, storage, and transmission, these analog signals need to be converted into digital form. Sampling make possible this conversion by taking a limited number of discrete data points from the continuous signal.

Sampling convert continuous-time, continuous amplitude signal into discrete-time continuous amplitude signal.

Analog signals are more susceptible to noise and external interference, which can degrade signal quality. Through sampling and subsequent digital processing, noise can be filtered out or reduced, resulting in cleaner and more reliable data.

What is the Sampling Theorem?

The sampling theorem, also known as the Nyquist-Shannon theorem, it is a fundamental principle that guides the process of converting analog signals to digital form.

The sampling theorem states that “if a signal is sampled at regular time intervals (ts), then the sequence of samples can be reconstructed or recreate the original signal. when the sampling rate is at least twice the highest frequency component present in the signal.”

Mathematically,

if a massage signal (continuous signal ) is denoted as m(t), and its highest frequency component is denoted as fm, then the sampling theorem states that to accurately reconstruct m(t) from its samples, the sampling frequency (or rate), denoted as fs, must be greater than or equal to twice the highest frequency component:

fs ≥ 2 * fm

When this condition is met, the original signal can be reconstructed from its samples using techniques like interpolation or various digital signal processing methods. The process of converting a continuous signal into discrete samples is known as “sampling” or “digitization.”

What is the Nyquist Rate?

The Nyquist rate, also known as the Nyquist frequency or Nyquist limit, is the minimum sampling rate required to accurately represent a continuous signal in a discrete form without introducing distortion or aliasing. It is a fundamental concept in signal processing and digital communication.

The Nyquist rate is defined as follows:

“The Nyquist rate is equal to twice the highest frequency component present in a continuous signal.”

Mathematically,

if the highest frequency component in a signal is denoted as fm, then the Nyquist rate, denoted as fs (the minimum sampling frequency), is given by:

fs = 2 * fm

If the sampling rate is less than the Nyquist rate, aliasing can occur, where higher-frequency components of the signal “overlap” into lower-frequency ranges, making it impossible to accurately reconstruct the original signal from the samples.

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What is sampling?

Sampling is a process of converting a continuous-time analog signal into discrete-time signal. This conversion is done with the help of sampler.

Why do we need to sample signals in digital communication?

Digital communication systems operate with discrete signals, and most information sources generate continuous analog signals. Sampling allows us to represent these analog signals in a digital format, making it easier to process, transmit, and store them.

Statement of sampling theorem

The sampling theorem states that “if a signal is sampled at regular time intervals (ts), then the sequence of samples can be reconstructed or recreate the original signal. when the sampling rate is at least twice the highest frequency component present in the signal.”
Mathematically,
if a massage signal (continuous signal ) is denoted as m(t), and its highest frequency component is denoted as fm, then the sampling theorem states that to accurately reconstruct m(t) from its samples, the sampling frequency (or rate), denoted as fs, must be greater than or equal to twice the highest frequency component:
fs ≥ 2 * fm

what is Nyquist rate?

The Nyquist-Shannon sampling theorem states that to accurately represent a continuous signal, the sampling rate must be at least twice the highest frequency component in the signal (Nyquist rate). It’s crucial to avoid aliasing and information loss during sampling.

How do I choose the right sampling rate for a signal?

Determine the highest frequency component (f_max) in your signal and choose a sampling rate (fs) that is at least twice f_max (fs ≥ 2 * f_max) to satisfy the Nyquist theorem.

What is transistor? Its Type working principle

What Is Transistor?

A transistor is a three-terminal electronic device that regulates the flow of electrical current or amplifies electronic signals. It is typically made of semiconductor materials like Silicon (Si), Germanium (Ge). It consists of three layers or regions: the emitter, the base, and the collector.

Transistors are used in electronic circuits to perform various functions, such as amplification, switching, and voltage regulation. They are a fundamental component in modern electronics and play a vital role in devices like computers, smartphones, televisions, and many other electronic systems.

Brief history of transistors

The development of the transistor can be attributed to the work of three scientists at Bell Laboratories in the United States: John Bardeen, Walter Brattain, and William Shockley. In 1947, they successfully created the first working transistor.

The invention of the transistor was a significant breakthrough in the field of electronics, as it replaced bulky and power-hungry vacuum tubes that were used for amplification and switching in electronic circuits at that time.

Transistors were much smaller, more reliable, and consumed less power than vacuum tubes. This breakthrough revolutionized the field of electronics and paved the way for the development of modern electronic devices.

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Parts of a transistor

A transistor consists of several key parts that work together to control the flow of electrical current or amplify electronic signals. The specific parts vary depending onhe type of transistor, but I’ll provide a general overview of the components commonly found in a bipolar junction transistor (BJT):

  1. Emitter (E): It is left regions in a BJT. It is moderately size. It is heavily doped (highly concentrated with impurities) to emit majority charge carriers (electrons for NPN and holes for PNP transistors) into the base region.
  2. Base (B): It is the center region between the emitter and the collector. It is thin and relatively lightly doped. It controls the flow of majority charge carriers from the emitter to the collector region by varying the amount of current or voltage applied to it.
  3. Collector (C): The collector is the third region (Right side) in a BJT. It is relatively large in size and moderately doped. It collects the majority charge carriers (electrons for NPN and holes for PNP) that flow through the base-emitter junction and allows them to exit the transistor.
  4. Base-emitter junction: This is the junction formed between the base and emitter regions. It acts as a diode, allowing current to flow from the emitter to the base when forward-biased (appropriate voltage applied) and blocking current in the reverse direction.
  5. Base-collector junction: This is the junction formed between the base and collector regions. It also acts as a diode and helps control the flow of current from the collector to the base region.

These are the fundamental parts of a BJT transistor.

Types of Transistors

There are two main types of transistors: Bipolar junction transistors (BJTs) and Field-effect transistors (FETs):

Bipolar junction transistors (BJTs)

Bipolar junction transistors (BJT) are classified into two types: NPN (negative-positive-negative) and PNP (positive-negative-positive) transistors.

NPN Transistors: In an NPN transistor, one p-type semiconductor material is sandwich between two n-type semiconductor material. In this configuration, the majority charge carriers are electrons. The emitter is doped with a higher concentration of electrons, while the base is lightly doped and the collector is moderately doped. When a small current flows into the base, it controls a larger current flowing from the emitter to the collector. In such a way, the device control the flow of current. NPN transistors are commonly used for amplification and switching purposes.

PNP Transistors: In a PNP transistor, one n-type semiconductor material is sandwich between two p-type semiconductor material. In this configuration, the majority charge carriers are holes. The emitter is doped with a higher concentration of holes, while the base is lightly doped and the collector is moderately doped. When a small current flows out of the base, it controls a larger current flowing from the emitter to the collector. PNP transistors also find applications in amplification and switching circuits.

Field-Effect Transistors (FETs):

Field-effect transistors control the flow of current using an electric field. They have three terminals: source, gate, and drain. FETs are further classified into several types, but the two most common are junction field-effect transistors (JFETs) and metal-oxide-semiconductor field-effect transistors (MOSFETs).

Junction Field-Effect Transistors (JFETs): JFETs have a doped semiconductor channel that connects the source and drain regions. The gate terminal controls the width of the channel, which influences the current flow. JFETs can be either N-channel or P-channel, depending on the doping types. They are primarily used for high input impedance applications, such as amplifiers and switches.

Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs): MOSFETs are the most widely used transistors in modern electronics. They have a metal-oxide-semiconductor structure with a gate terminal separated from the channel by an insulating layer (typically silicon dioxide). MOSFETs are further categorized as enhancement-mode (normally off) or depletion-mode (normally on) devices. They offer high input impedance, low power consumption, and excellent switching characteristics. MOSFETs are commonly found in microprocessors, memory devices, and digital circuits.

Transistor Terminals

A transistor has three terminals, each serving a specific function. The names of the terminals may vary slightly depending on the specific transistor type (NPN or PNP for BJTs, or NMOS or PMOS for MOSFETs), but the overall functionality remains the same. Here are the three main terminals of a transistor:

1.Emitter (E) / Source (S):

  • In a Bipolar Junction Transistor (BJT), the emitter is the terminal through which majority charge carriers (electrons for NPN and holes for PNP) flow into the transistor.
  • In a Field-Effect Transistor (FET), the emitter terminal is referred to as the source terminal.
  • The emitter/source terminal is typically marked with an arrow in the transistor symbol.

2. Base (B) / Gate (G):

  • The base terminal controls the transistor’s operation. It receives the input signal and controls the flow of charge carriers between the emitter and collector terminals.
  • In a BJT, the base terminal is responsible for injecting minority charge carriers (electrons for NPN and holes for PNP) into the base region, allowing or blocking the current flow between the emitter and collector.
  • In an FET, the base terminal is known as the gate terminal and controls the conductivity of the channel between the source and drain terminals.
  • The base/gate terminal is usually represented by a straight line in the transistor symbol.

3. Collector (C) / Drain (D):

  • The collector terminal collects the majority charge carriers (electrons for NPN and holes for PNP) that flow through the transistor.
  • In a BJT, the collector terminal is responsible for the majority carrier collection, allowing the transistor to provide amplification or switching capabilities.
  • In an FET, the collector terminal is called the drain terminal, and it receives the current from the channel between the source and drain terminals.
  • The collector/drain terminal is often represented by an arrow pointing outward from the transistor symbol.

These three terminals work together to control the flow of current through the transistor and enable its amplification or switching behavior. It’s worth noting that the names and symbols for these terminals may vary depending on the transistor type, but their functions remain consistent across different transistor families.

Working Principle of Transistor

There are two main types of transistors: the bipolar junction transistor (BJT) and the field-effect transistor (FET). I’ll provide a brief overview of the operation of each type:

Bipolar Junction Transistor (BJT): The operation of a Bipolar Junction Transistor (BJT) involves the control of current by a small input current at the base terminal.

There are two types of BJTs: NPN and PNP, with slightly different behaviors, but the basic operation principles remain the same. Here’s a detailed explanation of the operation of an NPN BJT:

The BJT operates in three different modes: Active Mode (amplification), Cutoff Mode and Saturation Mode (switching).

  1. Active Mode: In the active mode, the BJT is used as an amplifier. A small current flows from the base-emitter junction, which controls a much larger current flowing between the collector and emitter. By varying the current at the base-emitter junction, the BJT can amplify or switch electrical signals. Small base current (Ib) controls a much larger collector current (Ic).
  2. Cutoff Mode: In the cutoff mode, the BJT is effectively switched off, and the collector current is minimal. The base-emitter junction is reverse-biased (Vbe < 0), preventing the flow of base current (Ib) and effectively isolating the collector and emitter regions. Without the flow of base current, there is no amplification, and the collector current (Ic) reduces to a negligible value.
  3. Saturation Mode: In the saturation mode, the BJT operates as a fully conducting switch. A forward bias voltage (Vbe) is applied to the base-emitter junction, allowing a significant base current (Ib) to flow. The base current enables a large collector current (Ic) to flow freely between the collector and emitter terminals. In this mode, the BJT acts as a closed switch, with minimal voltage drop across the collector-emitter junction.

Field-Effect Transistor (FET): FET transistors are based on the principle of controlling the conductivity of a semiconductor channel using an electric field.

FETs are primarily of two types: the junction field-effect transistor (JFET) and the metal-oxide-semiconductor field-effect transistor (MOSFET).

  • In a JFET, a voltage applied between the gate and source terminals creates an electric field that controls the width of the conducting channel between the source and drain terminals.
  • In a MOSFET, a thin insulating layer (oxide) separates the gate from the conducting channel, which can be either positively or negatively doped.
  • By applying a voltage to the gate terminal, the FET controls the conductivity of the channel, allowing it to amplify or switch electronic signals.

In both types of transistors, the control of current or voltage at one terminal (base/gate) allows the transistor to control or amplify the current or voltage at another terminal (emitter/collector or drain/source). This functionality enables transistors to perform a wide range of functions in electronic circuits, including amplification, signal processing, digital logic, and power regulation.

What is a transistor?

transistor is a three-terminal electronic device that can amplify or switch electronic signals and electrical power. It is a fundamental building block of modern electronic devices and circuits.

What are the main types of transistors?

The two main types of transistors are Bipolar Junction Transistors (BJTs) and Field-Effect Transistors (FETs). BJTs include NPN and PNP transistors, while FETs include Junction Field-Effect Transistors (JFETs) and Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs).

What is the difference between an NPN and a PNP transistor?

The main difference lies in the arrangement of the semiconductor layers. In an NPN transistor, the layers are P-N-P, while in a PNP transistor, the layers are N-P-N. The behavior and operation of NPN and PNP transistors are similar, but the polarities of voltages and currents are reversed.

How does a transistor amplify signals?

Transistors amplify signals by controlling a larger current or voltage with a smaller input signal. In the case of a BJT, a small base current controls a much larger collector current. In an FET, a small voltage applied to the gate controls the current flow between the source and drain terminals.

How does a transistor work as a switch?

ransistors can work as switches by operating in either the cutoff or saturation mode. In the cutoff mode, the transistor is switched off, and there is no current flow. In the saturation mode, the transistor is fully conducting, allowing a large current to flow.

What is the difference between a JFET and a MOSFET?

JFETs and MOSFETs are two types of FETs. The main difference is the way the control voltage is applied. In a JFET, a voltage is applied directly between the gate and source terminals. In a MOSFET, a voltage is applied between the gate and source terminals through an insulating layer (oxide).

What are the typical applications of transistors?

Transistors find widespread use in various applications. They are used in amplifiers, audio systems, radios, televisions, computers, digital circuits, power supplies, motor control, and many other electronic devices and systems.

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Web Development

Learning web development (Front end) you should know following

  1. HTML
  2. CSS
  3. Java Script

I will explain framework also

  1. Angular– a java script framework

2. Tailwind – a css frame work

ELECTRICAL ENGINEERING MCQ

This questions are very help full in your JE/AE exam electrical engineering MCQ

Question 01: Which material is used for the manufacture of brushes in DC motors?

A. Lead
B. Copper
C. Carbon
D. All of these

Answer: Carbon

Question 02: Which among these devices are used to protect low voltage induction motor?

A. HRC fuse
B. Contactor starter
C. Thermal overload relay
D. All of these

Answer: All of these

Question 03: Tap changing transformers are used for……….

A. stepping up the voltage
B. stepping down the voltage
C. both stepping up and stepping down the voltage
D. supplying low voltage current for instruments

Answer: both stepping up and stepping down the voltage

Question 04: An ammeter is a …………….. instrument.

A. Absolute instrument
B. Secondary instrument
C. Recording instrument
D. Integrating instrument

Answer: Secondary instrument

Question 05: For what voltage is Twin conductor bundle used in India?

A. 220 kV
B. 330 kV
C. 500 kV
D. 750 kV

Answer: 500 KV

Question 06: Which of the following machine will be preferred to charge the batteries?

A. Series motor
B. Shunt generator
C. Series generator
D. Series generator

Answer: Shunt generator

Question 07: Which of the following motors is used in ceiling fan?

A. Universal motor
B. Induction motor
C. Series motor
D. Synchronous motor

Answer: Induction motor

Question 08: Electrostatic voltmeter instruments are suitable for ……………

A. AC work only
B. DC work only
C. Both AC and DC work
D. None of these

Answer: Both AC and DC work

Question 09: The failure % of electric motor is higher due to………….

A. Insulation failure
B. Over loading
C. Bearing failure
D. None

Answer: Bearing failure

Question 10: At what rated voltage is the shielded cable provided in a low voltage system?

A. Rated voltage < 1kv

B. Rated voltage > 1 kv
C. Rated voltage < 500 kv
D. None of them

Answer: Rated voltage < 1kv

Question 11: What is the given symbol represents in electrical system?

A. UPS
B. Rectifier
C. Inverter
D. Battery

Answer: Inverter

Question 12: Which among these is the application of universal motors?

A. Fans
B. Washing machines
C. Hair dryers
D. Vacuum cleaners

Answer: Vacuum Cleaners

Question 13: Which of the amongst is the first equipment placed in the uninterrupted power supply (UPS)?

A. Inverter
B. Battery
C. Rectifier
D. Any of these

Answer: Rectifier

Question 14: Which material has a lower dielectric strength at 50 Hz?

A. Bakelite
B. Glass
C. Air
D. Dielectric oil

Answer: Air

Question 15: Which material is used for the manufacture of brushes in DC motors?

A. Graphite
B. Lead
C. Copper
D. All of these

Answer: Graphite (or carbon both correct)

Question 16: Which among these is a type test?

A. Bending test
B. Drainage test
C. Dielectric security test
D. All of these

Answer: All of these 

Question 17: In a transformer,………is found by the short circuit test.

A. Copper loss
B. Hysteresis loss
C. Eddy current loss
D. Iron loss

Answer: Copper loss

Question 18: Non-loading heat run test on transformer is performed by means of

A. SC teat
B. OC test
C. Core balance test
D. Sumpner’s test

Answer: Sumpner’s test

Question 19: In Transformer, oil is used for

A. Cooling the Transformer
B. Providing insulation to Transformer winding and for cooling the Transformer
C. Lubricating the Transformer
D. None

Answer: Providing insulation to Transformer winding and for cooling the Transformer

Question 20: Which material can be used upto a temperature of 130° C?

A. Mica
B. Cotton
C. Synthetic resin
D. All of these

Answer: Mica