Wednesday, May 1

Energy Bands in Silicon


Introduction to Energy Bands in silicon:

Before we start with energy bands in silicon,  let us know about energy bands.The energy band of any solid is a structure which describes the allowed and the forbidden values of energies for that solid. The energy band is a function of the diffracted quantum mechanical electron waves which are present in a periodic crystal lattice which have a specific crystal system and specific Bravais lattice.

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Reason behind formation of energy band in elements like silicon


As the electrons of any single isolated atom occupy several atomic orbitals which are in the form of set energy level that are discrete. If a molecule is formed by several atoms, which are brought together, the atomic levels of the atoms split and form a coupled oscillation. Similarly if a large number of atoms of the order of 1020 or more are brought together in the form of a solid, the atomic levels are very large in number and the energy difference between the two energy levels is very small which give rise to a continuous band of the energy levels.


Description of Energy Bands in Silicon


The Fermi level is one of the important levels in the energy band of any material because it determines the nature of the material i.e. the material is conductor or insulator or the semiconductor. The silicon is a semiconductor material and for it the Fermi level is exists essentially in the halfway between the valence and the conduction bands of the silicon. In silicon at 0 K temperatures there is no conduction of electron but at finite temperatures the electrons moves from valence band to the conduction band and the number of electrons which reaches the conduction band contributes for the flow of current in silicon and this current can be modeled by Fermi function.

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Conclusion for Energy Bands in Silicon


There are some intervals in the energy bands which contain no levels or the orbitals these interval forms the energy band gaps. The energy bands of any material determine several characteristics like the electronic and the optical properties of the material.

Thursday, April 25

Elements of a Communication System


Introduction:

Communication system is used to conveying a message from one person to other. By means of an information is the attach which holds people jointly. A communication system is known as grouping of processors and hardware used to bring about the transfer of message through communication. This system having some elements for transfer the signal from source to destination.

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Communication Systems:

A communication system is known as grouping of processors and hardware used to bring about the transfer of message through communication. This process of a system allows us to take total unit.

An energy is need to start the system. The control mechanism regulates the process. That is, it manipulates the message input into whatever form is necessary. The result of this method is the appearance of message in a form which will permit us for communication to take place.

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Elements of communication systems

Let us see about elements of communication systems,

Transmitter:

It is used for modulation and coding the original signal.
In communication system elements, it is used to converting an electrical signal into a form which is comfort for transmission on the physical channel or transmission medium.


Channel:

In communication system elements, the communications channel is known as a communication medium.
It is used to send the signal from the transmitter to the receiver.
The Receiver:

In communication system elements, It is used for demodulation such as decoding the signal from channel.
The receiver is used to recover the message signal enclosed in the received signal.
Noise:

In communication system elements, noise is produced at transmitter due to two process
1. Natural resources 2. Manmade

By nature, such as radiation from sun By manmade, noise made from like vehicles.
This noise can be reduced by using filter.

Wednesday, April 24

Initial Velocity


Let us start with the difference between velocity and speed. It is quite obvious after all the discussion about vector and non vector quantities. Speed is basically a measurement with no direction. In case of velocity we also consider direction.

Velocity can be of two types: initial velocity and final velocity. When the object starts its motion then we can say that the initial velocity is zero as it has just started from rest. Similarly we can also consider int. velocity as some constant value. Let us take an example of a car starting from rest and attaining a velocity of 50 km per hour in 1 hour time period.

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So here we can say that the int. velocity of the car is zero and the final velocity is 50 km per hour, directed northwards. Here mentioning the direction is very important as velocity is all about direction, it being a vector quantity.

Let us now discuss Initial velocity formula. We have 3 equations of motion that have a reference to int. velocity and hence can be used for its calculation.
They are as follows:
V = u + a t ------------ > (1)
Here v is the final velocity
U is the int. velocity
A is the acceleration
T is the time period.
So u = v – a t
Also the second equation is
S = u t + 1.5 a t^2 - - - - - - >(2)
Here s is the distance covered in time interval t.
A is the acceleration
We also have a third equation for calculating velocity. It is as follows:
V^2 = u^2 + 2 a s - - - - - - -> (3)

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Here v is the final velocity and a is the initial velocity.
All these are initial velocity equation. We can also say that u^2 = v^2 – 2 a s - - - - - - - > (4)
Let us take a real world example to clear the concept. Let us assume the final velocity of the car is 50 m per sec and the time taken to complete the journey is 2 hours. Also the acceleration is 10 meter per second square. So now using first formula we will try to calculate the initial velocity.
Hence v = u + a t
Or 50 = u + 20
U = 50 – 20 = 30 m per sec

Inertia


Newton’s first law of motion explained that if an object is in rest then it is said to be in rest and when it is moved then it is in motion, so it proves that all objects have natural tendency to be in rest, they resist their motion.

So the property of any object to stop its state of motion is known as inertia. This word can also be described in terms of a resistance in the motion of object. So this is the particular property of an object to stop any alteration in its motion. Please express your views of this topic Angular Acceleration Problems by commenting on blog.

It is basic of classical physics and use to know about the matter’s motion and the effect of applied forces on the motion of matter. In general words, this can also be explained as the resistance to alter in the value of the velocity or the momentum. There is not any particular theory that describes the source of (In).
The law of inertia states the same definition of (In). This explains it as the specific property of any object to stop any change in its motion. As Newton's states that for the movement of an object, the external force is required like friction or gravity.

So first this concept was explained with taking the example of earth as the earth also revolves around the sun. And if the body is moved on a flat surface in a given straight direction then it is continued with its speed with the same direction unless disturbed.

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The Inertia Equation can be written with the use of mass and radius of moving body. So the formula for the (I) may be generally expressed as; I = k m r^2; where m is the mass of body, r is the distance travelled, and k is (I) constant which depends on the shape of the moved body.
For example; if we discuss about the thin-walled hollow cylinder, then the momentum of a thin-walled hollow cylinder is like the point mass. So it can be expressed as; I = m x r^2  and k is equal to one as it is taken one for point mass, where m is hollow’s mass and r is for distance.

Here we are taking two distances; one is the distance between axis and the thin walled hollow and ro is the distance between axis and outside hollow. So for the hollow cylinder: I = 1/2 m (ri2 + ro2). But for a solid cylinder, it is equal to the; I = 1/2 m r^2 (3c).
We can also measure the Product of Inertia by measuring (I) of a moving body in two different axes.  As it is measured by the mass of an object, so the Units of Inertia is kgm2. This is Inertia Units in SI system.

Uses of Solar Energy


Introduction to solar energy

Sun is the primary source of heat and light, all living things need sunlight for it's survival, we are getting various forms solar radiations like UV radiations, gamma radiations,infraded radiations etc, solar energy can be used as various other forms of energy,so, we can use solar energy as alternative sources of energies.In 21st century, obviously we should depend upon alternative sources of energy,because some sources of energy are  limited in nature, so it is known non-renewable sources of energy like fossil fuels,by considering these situations, we should depend upon renewable sources of energy like solar energy.

Solar energy  be used to run vehicles, in solar lights,in solar traffic signals, in solar water heaters, in solar cookers,plants prepare food by the process of photosynthesis using solar energy etc.

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Applications of solar energy


Solar water heaters

Solar water heaters are really boon to the mankind, which conserves other sources of energy and it is eco friendly, in solar water heater it has solar panels consisting of photovoltaic cells,semi conductors, which are made out of silicon chips. these silicon chips absorb solar energy and help in heating up the water, there is an arrangement of inlet and outlet for water. water has to pass through in these set up of solar water heater.

Solar heating system composed of solar thermal collectors, a water storage tank, interconnecting pipes and a fluid system to move the heat from the collector to the tank, so in this process heating up the water by using direct sunlight, no electricity is required.

we can use this solar water heating system for various purposes like under floor heating, heating swimming pools, energy input for space heating or cooling, storing solar energy for future like for winter season by storing solar heat in the ground.

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Solar vehicles


Solar energy can be used to run vehicles like solar bicycle, solar cars, solar autos etc, these vehicles proved and it may replace our existing needs to run vehicles ,basically a solar vehicle is a electrically powered by solar energy. the photovoltaic cells absorb solar energy, then which converted to electrical energy.

Thursday, April 18

Kinds of Forces


Introduction to kinds of force:
Sir Isaac Newton was the first who gave an exact definition of force.He stated that :

Force is the external agency applied on a body to change its state of rest and motion.

There are four basic kinds of forces in nature. They are

Gravitational force
Electromagnetic force
Strong nuclear force
Weak nuclear force
Lets see a brief explanation of the different kinds of forces.

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Explanation of gravitational and electromagnetic forces:


Gravitational force:

It is the force between any two objects in the universe. It is an attractive force by virtue of their masses. By Newton's law of gravitation, the gravitational force between tow bodies is directly proportional to the product of their masses and inversely proportional to the square of the distance between them. Gravitational force is the weakest force among the fundamental forces of nature but has the greatest large- scale impact on the universe. Among the basic force only gravity works universally on all matter and energy, and is universally attractive.

Electromagnetic force:

It is the force between charged particles for example the force between two electrons, or the force between tow current carrying wires. Electromagnetic forces for like charges is repulsive and for unlike charges is attractive. The electromagnetic force obeys inverse square law. It is very strong compared to the gravitational force. It is the combination of electrostatic and magnetic forces.

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Explanation of strong and weak nuclear forces:


Strong nuclear force:
It is the strongest of all the basic forces of nature. It, however, has the shortest range, of the order of 10-15 m. This force holds the protons and neutrons together in the nucleus of an atom.

Weak nuclear force:
Weak nuclear force is important in come types of nuclear process such as `beta` -decay. This force is not as weak as the gravitational force.

Wednesday, April 17

Average Speed


Average Speed

When a body moves, sometimes it accelerates and other time it decelerates due to the traffic congestion on the road, so the speed of the body is not constant over the whole journey and keeps on changing with respect to several factors.
If we need to calculate the speed for the entire journey it is calculated by finding the total distance travelled and the time taken to travel it. This is known as the average speed of the body for the journey it has travelled.

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Average Speed Formula

The formula for finding the avg speed is;
Saverage = (total distance travelled / total time taken);
where, total distance travelled is equal to the distance between the source and destination of the body and the total time is the time taken to move between the source and destination by the body.

Formula for Average Speed
The formula of avg speed is as follows;
Saverage = (DTotal / TTotal);
DTotal = Total distance travelled the body;
TTotal = Total time taken in travelling the distance DTotal by the body.

Average Speed Definition

The avg speed is defined as the average of the speed of the body over the total distance travelled by it. The body might be travelling at different speed over the portion of the total distance but it maintains the avg speed for the entire journey as constant. The avg speed can be obtained by dividing the distance travelled by the object by the time taken to the distance.
Average is helpful in identifying the speed of the body when it is travelling at different speeds for the different portions of journey. It is used to calculate the speed of the object in varying traffic conditions.

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What is Average Speed

To understand the average let us take an example. A truck is climbing the hill at the speed of 15 km/hr for 1 hour and then it started to slow down as the hill is steeper and travels at 5 km/hr. After 2 hours the truck started to climb down the hill at the speed of 25 km/hr for 1 hour to completely come to the plain.
In this journey as we see the truck is moving at different speed at different time and hence it is difficult to identify the speed of the truck but if divide the total distance travelled by it with the total time it took to travel the total distance then what we obtain is the avg speed.
In this example the avg speed is
Avg speed = 50 / 4 = 12.5 km/hr.