# Archive for April, 2011

## Scalar and vector analysis

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Let us discuss today about two quantities called scalars and vectors. Suppose you are going in your car or bike. Your vehicle must have speedometer which shows the speed. Let the speed is 60 km/hour. Now suppose you have certain instrument which shows that you are going in north direction with 60 km/hour.

So the 60 km/hr means only the magnitude or value. So the quantities which have only magnitudes or values are called scalars.

But the 60 km/hr in north direction means the quantity has value as well as direction in it. These quantities are called vector quantities.

Therefore the more technical definitions will be: (more…)

## Applications of electromagnetic field theory

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Electromagnetic Field Theory has applications in analysing and designing of communication system like:

• Satellite Communication
• TV Communication
• Wireless Communication
• Mobile Communication
• Microwave Communication
• This theory is also used in analysis and designing of antenna, transmission
• lines and wave guides. (more…)

## Difference between circuit theory and electromagnetic field theory

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Circuit Theory: As the name suggests, circuit theory deals with electrical circuit. An engineer can predict the performance of complicated electrical networks with the help of circuit theory. But this theory has certain limitations like :

• It cannot be applied in free space.
• It is useful only at low frequencies.

This theory is unsuccessful in explaining the radiation of electromagnetic waves into space in radio communications.

It cannot be used to analyse or design a complete communication system. Example: Radio Communication System.

Electromagnetic Field Theory. Although electromagnetic Field Theory (EMFT) is complex in comparison with circuit theory but EMFT is simplified by using appropriate mathematics. This theory deals with E and H vectors, whereas circuit theory deals with voltages and currents.
This theory has following advantages in comparison to circuit theory:

• It is also applicable in free space.
• It is useful at all frequencies, particularly at high frequencies,
• The radiation effect can be considered.
• This theory can be used to analyse or design a complete communication system. Example: Wireless Communication, Radio Communication.

## Construction of semiconductor laser

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In the last article, I have explained the basics of semiconductor. Today I will explain the construction of a semiconductor laser.

Example of semiconductor laser: One of the examples of semiconductor lasers is gallium arsenide (GaAs). It is heavily doped semiconductor. Its n-region is formed by heavily doping with tellurium in a concentration of 3 x 1018 to 5 x 1018 atoms/cm3 while its p-region is formed by doping with zinc in concentration around 1019 atoms/cm3.

Active medium:

## Beant college of engineering and technology gurdaspur

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Name of the Institute: Beant College of Engineering & Technology is situated in the city Gurdaspur (Punjab) of India.

Affiliated with: Punjab Technical University (PTU), Kapurthala

Approved by: All India Council for Technical Education (AICTE), New Delhi.

Courses offered:

## Baba Kuma Singh Ji Engineering college Amritsar

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Name of Institute: Baba Kuma Singh Ji Engineering college is situated in the city Amritsar (Punjab) of India.

Affiliated with: Punjab Technical University (PTU), Kapurthala

Approved by: All India Council for Technical Education (AICTE), New Delhi.

B.Tech. Courses offered:

## Semiconductor laser

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Before discussing the construction and working of semiconductor laser, let us discuss the review of semiconductors as it will be necessary for you to write the basics of semiconductors in case of exams:

A semiconductor is a material whose conductivity lies between those of conductor and insulator. Semiconductors are of two types:

a) Intrinsic semiconductors or pure semiconductors

b) Extrinsic semiconductors or doped semiconductors

Extrinsic semiconductors are further classified into two types depending upon the type of majority carriers:

i) n-type semiconductors where electrons are majority carriers.

ii) p- type semiconductors where holes are majority carriers.

When a p-type semiconductor and a n- type semiconductor is joined by special techniques, there will be flow of electrons from n side to p side and flow of holes from p side to n side. After some time, an electric field will be created which will oppose this flow and flow stops. Thus, there will be formation of depletion region. This region is called so because it is depleted from charge carriers.

Note: In next article I will explain the construction of semiconductor laser. In case of any problem in this article or any other physics article, kindly post in the comment section.

## wavelength, output and applications of carbon dioxide laser

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Why helium is doped in carbon dioxide laser:

The CO2 molecules in the states E4 and E3 deexcite to state E2 through inelastic collision with unexcited CO2 molecules. This process is very fast so there will be accumulation of CO2 in this level and they can break the population inversion in upper levels because there is probability of excitation of molecules from E2 to E3 and/ or E4.

To stop the accumulation of CO2 molecules in E2 special additives like He and water vapors are added into the gas mixture. CO2 molecules return to the ground state E1 through collisions with the He to which it transfers the excitation energy. (more…)

## Working of cabon dioxide laser

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In the earlier articles, I have explained the modes and construction of carbon dioxide laser. Today I will explain the working of the carbon dioxide laser.

Pumping of nitrogen molecules: As electric discharge is used as pumping source and when electric discharge is passed through the mixture of CO2, N2 and He, electrons are accelerated down the tube. These accelerated electrons collide with the N2 molecules and excite them to higher vibrational energy levels. Let us say the N2 excited from level F1 to F2.

## Construction of carbon dioxide laser

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In the previous article, I have explained the various modes of carbon dioxide and about the significance of these modes in carbon dioxide laser. Today I will discuss the construction of carbon dioxide laser.

Carbon dioxide laser consists of a discharge tube having a diameter of 2.5cm and a length of about 5m. The discharge tube is filled with a mixture of carbon dioxide, nitrogen and helium gases in the ratio of 1:2:3 with water vapors. Pressures maintained are about P (for He)= 7 Torr, P (for N2)= 1.2 Torr and P (for CO2 = 0.33 Torr).

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