Electronics Engineering

Kirchoffs Current Law : [KCL]

This law is also called Kirchhoff's point rule, Kirchhoff's junction rule (or nodal rule), and Kirchhoff's first rule. The principle of conservation of electric charge implies that: : At any point in an electrical circuit that does not represent a capacitor plate, the sum of currents flowing towards that point is equal to the sum of currents flowing away from that point. Kirchoffs Voltage Law : [KVL]

This law is also called Kirchhoff's second law, Kirchhoff's loop (or mesh) rule, and Kirchhoff's second rule. : The directed sum of the electrical potential differences around any closed circuit must be zero.

Kirchoffs Laws are widely used in the Electrical and Electronic engineering fields.

Hope this helps =)

3: emitter, base, collector

There are three regions but to be absolutely picky I think only two of them need be doped.

Nope: they MUST be doped NPN or PNP. If any are undoped it will not function as a transistor.

Electricity does not flow in open circuit because the path is not a complete circuit and has the maximum impedance to flow of electricity while it flows in short circuit because electricity always wants a path with least impedance to flow which short circuit is one of such path

Current can jndeed flow through an open circuit. A capacitor is an open circuit, yet it will allow a d.c. current to flow for a short period of time, and an a.c. current can flow continuously.

MODULATION:

Usually, the signal that we want to transmit, say a speech signal with 4000 Hz frequency, will require a very big antenna. For any signal the frequency f is related to wavelength Las

c = L * f ………………………… (i)

Where c is velocity of light. And antenna length is generally taken as L/2 which simply means for our case antenna length is 75000 m, obviously this size of antenna is too big to use on day to day basis. That is why we take our speech signal or the desired signal and take another high frequency signal known as carrier (carrier can be any signal but should have high frequency and in practice we use a simple continuous wave signal), now we alter one or more parameters of this career signal in accordance with our desired signal, this parameters can be any one or combination of parameters. The basic parameters are amplitude, frequency, and phase of the signal. The result of this alteration we get is known as modulated signal, the desired signal which we wanted to transmit is known as modulating signal also known as base band signal and modulated signal is also known as band pass signal. The whole process is known as MODULATION.

There are many types of modulation starting from amplitude modulation popularly known as AM, frequency modulation (FM), QPSK, PCM, GMSK, QAM etc.

MULTIPLEXING:

Basically there are two types of system, time domain and frequency domain. In time domain we transmit frames, and in frequency domain we transmit in accordance with frequency. Now if there is more than one source of signal and we want to transmit them together then we implement multiplexing. In multiplexing we mix the source signals (off course with some precautions) say if we want to mix them in time domain then our frame will contain some packets form source A and some packets from source B and so on depending upon the constraints of the channel and time frame. The signals that source are generating can either be modulated signals or we can even send our multiplexed signal to the modulator and then modulate the signal. At the receiving end be demultiplex the signals. In multiplexing we do not provide a dedicated resource to a single source. I.e. we do not dedicate the complete time frame to a single source (in our case it is time frame). Multiplexing is also seen as you are travelling on a four lane road and suddenly it get narrower and turned to single lane, at this point the traffic police will allow one car from each lane to drive through that narrow single lane, this is what we called MULTIPLEXING.

MULTIPLE ACCESS:

As the name suggest, multiple access means multiple users can access the channel or link. Multiple access provides dedicated resources to the user (with a time constraint) in comparison to the multiplexing which does not provide any type of resources. There are many type of Multiple access schemes like FDMA frequency division multiple access, TDMA time division multiple access, CDMA code division multiple access, SDMA space division multiple access etc. take the example of FDMA, the whole frequency band is divided into small frequency bands called channels, now each channel is having certain capacity to take the traffic say a channel can accommodate single user at time, then the whole frequency bandwidth can be access by as many users as there are channels, mathematically if we are having a bandwidth of 200 KHz and channel bandwidth is 50 KHz then it means we can accommodate 4 users at a time by giving 50 KHz channel to each. This is so called multiple access, i.e. multiple users can access the bandwidth simultaneously and we do not require any additional hardware at the receiving end to separate the desired user from the other users as we do in Multiplexing. In reality the concept of Multiple Access is more complicated and In GSM each channel can accommodate 8 users at a time and each channel has 200 KHz bandwidth.

Even I am searching its answer. But, I feel, multiplexing is technique and multiple access is way to use this technique.

but there is a difference between multiple access and multiplexing that should be noted:

Multiple access refers to the remote sharing of a communication channel such as a satellite or radio channel by users in highly dispersed loctions. on the other hand, multiplexing refers to the sharing of a channel such as a telephone channel by users confined to a local site.

Modern telephone networks allow bandwidths in their channels that are much larger than those is needed for a digitalized telephone channel. Basically, a number of channels share a common transmission medium with the aim of reducing costs and complexity in the network. Multiplexing is defined as the process by which several signals from different channels share a channel with greater capacity. When the sharing is carried out with respect to a remote resource, such as a satellite, this is referred to as multiple access rather than multiplexing.

According to the definition described in Encyclopedia of Britinica : Multiplexing is defined as the sharing of a communications channel through local combining at a common point. In many cases, however, the communications channel must be efficiently shared among many users that are geographically distributed and that sporadically attempt to communicate at random points in time. Three schemes have been devised for efficient sharing of a single channel.

Martin Cooper invented the cell (mobile) phone. He was the first one to make a call and speak on his moble phone.

Mr Cooper, born December 26, 1928, wanted people to be able to carry their phones with them anywhere. While he was a project manager at Motorola in 1973, Cooper set up a base station in New York with the first working prototype of a cellular telephone, the Motorola Dyna-Tac. After some initial testing in Washington for the F.C.C., Mr. Cooper and Motorola took the phone technology to New York to show the public.

The First Cellphone (1973)

Name: Motorola Dyna-Tac

Size: 9 x 5 x 1.75 inches

Weight: 2.5 pounds

Display: None

Number of Circuit Boards: 30

Talk time: 35 minutes

Recharge Time: 10 hours

Features: Talk, listen, dial

See related links for further information on Martin Cooper and his invention.
The idea of the cell phone began in the 1920's with police radios, but it wasn't until 1947 that the first one was made by Bell labs. In 1974 Dr. Martin Cooper is given credit for the cell phone that is most like the ones we have today. He was working for Motorola at the time. The phone was only for government use and in 1984 it was sold to the public for the first time. The early cell phones were large, heavy, and copied land line phones in style. They were carried in a zippered bag with the whole bottom as the battery.
The cell phone was first thought of in the 1920's when the use of police radios began. In 1947 Bell Labs made the first cell phone, but it took Dr. Cooper of Motorola to make a cell phone in 1974 for the government. The public use of cell phones began in 1984.
Your question has two answers. The phone was invented in 1889 by Bell. The cell phone idea began in the 1930's, but in 1947 Bell Labs made a cell type phone. The first cell phone inventor id given to Dr. Martin Cooper of Motorola in 1974. This phone was sold to the government. The public did not get it until 1984.
It was made by Bell labs in 1947, but the man given the most credit for it is Dr. Martin Cooper who made one very much like what we have today in 1973.
We knew someday everybody would have one. Martin Coopercreated the "DynaTAC," the first commercial cell phone, which hit the market in 1983. (CNN) -- In 1973, Martin Cooper changed the world, although he didn't know it yet. With the invention there was concern regarding brain cancer due to the fact that cell phones send out high frequency of radio waves.
It was invented by Will Maacmillan in 1969
—Doctor Martin Cooper invented the modern cell phone. He invented the technology responsible for the cell phone when was the Director of Research and Development at Motorola. Cooper is also known as the first person to make a call on a cell phone. His groundbreaking call took place in April of 1973 in New York. He is currently the CEO of an antenna corporation.