Electricity is a very broad topic. For this post, i shall be focusing more on static electricity, where a charge is built up and transferred to another body through a very short time. This is often called "transient current".
The static charge can be produced by rubbing two objects together. In any static electricity occurrence, it is always the electrons that move and not the positive charges. Thus when we say a positive charge is produced on an object, we ar actual saying that the electrons moved out of the object, thus giving it an overall positive charge.
There is also a very important concept called "earthing". Earthing of an object can neutralise the charge on it. For example, if we earth a positively charged object, the electrons from the ground would come up to the object's positive charges and neutralise them.
Thursday, August 13, 2009
Tuesday, August 11, 2009
P- and N- type semiconductors
The P in P-type and the N in N-type stand for positive and negative respectively.
P-Type semiconductor
The addition of trivalent impurities such as boron to the semiconductor creates holes. As can be seen, the acceptor impurity creates a hole as indicated by the arrowed circle.
N-Type Semiconductor
To illustrate how the N-type doping is like, we can look at the example below.
The addition of pentavalent impurities such as Antimony contributes free electrons, greatly increasing the conductivity of the semiconductor.
Similarly, the explanation of what an acceptor is -
The process of doping a semiconductor with an impurity which has fewer protons per atom (fewer electrons per atom) is done with the semiconductor accepting electrons from the impurity, thereby rendering the semiconductor an acceptor.
The atoms in a semiconductor will form bonds with neighbouring atoms in such a manner that each atom sees a “closed shell”. Since the acceptor atom introduces fewer electrons, the shell is not closed; all of the electrons are tightly bound. If an additional electron can be found, it will tend to fit the shell. The semiconductor atoms that have lost an electron are known as holes.
An acceptor-doped semiconductor is called a P-type semiconductor because it has positive charge carriers.
The purpose of P-type doping is to create an abundance of holes.
Bands for Doped Semiconductors
The application of band theory to N-type and P-type semiconductors shows that extra levels can be added by impurities. In N-type materials, there are electron energy levels near the top of the band gap so that they can easily move into the conduction band. In P-type materials, extra holes in the band gap allow electrons from the valence band, leaving mobile holes in the valence band.
The application of band theory to N-type and P-type semiconductors shows that extra levels can be added by impurities. In N-type materials, there are electron energy levels near the top of the band gap so that they can easily move into the conduction band. In P-type materials, extra holes in the band gap allow electrons from the valence band, leaving mobile holes in the valence band.
continued...
As a continuation of the semiconductors, i will be covering the "dopes" today.
Doping:
The ability of conductivity of semiconductors can be controlled by doping the materials with impurities. The number of impurity atoms added may be by the thousand or million folds. The term low doping means small number of atoms added in the order of one per 100 million atoms. High doping is that of bigger number of atoms added in one per ten thousand atoms. Other than the number of atoms of impurities added, the type of impurity also affects conductivity. Varying the number and type of impurity atoms may be done in thousands or millions folds too.
Dopants
The materials chosen as suitable dopants depend on the atomic properties of both the dopant and the material to be doped. Generally, dopants that produce desired controlled changes are either electron donors or acceptors.
This may sound very technical but let me attempt to explain what a donor is.
This is the process of doping a semiconductor with an impurity which has more protons per atom (more electrons per atom). The atoms in a semiconductor will form bonds with neighbouring atoms in such a manner that each atom sees a “closed shell”. Since the donor atom introduces an additional electron, this electron is loosely bound; it is more free to move than the electrons which form the closed shell. This additional electron is easily put into the conduction band and can therefore conduct electricity easily. A donor-doped semiconductor is called an N-type semiconductor because it has negative charge carriers.
In other words, when a doping material is added, it gives away (donates) weakly-bound outer electrons to the semiconductor atoms. The purpose of N-type doping is to produce an abundance of mobile or “carrier” electrons in the material.
Doping:
The ability of conductivity of semiconductors can be controlled by doping the materials with impurities. The number of impurity atoms added may be by the thousand or million folds. The term low doping means small number of atoms added in the order of one per 100 million atoms. High doping is that of bigger number of atoms added in one per ten thousand atoms. Other than the number of atoms of impurities added, the type of impurity also affects conductivity. Varying the number and type of impurity atoms may be done in thousands or millions folds too.
Dopants
The materials chosen as suitable dopants depend on the atomic properties of both the dopant and the material to be doped. Generally, dopants that produce desired controlled changes are either electron donors or acceptors.
This may sound very technical but let me attempt to explain what a donor is.
This is the process of doping a semiconductor with an impurity which has more protons per atom (more electrons per atom). The atoms in a semiconductor will form bonds with neighbouring atoms in such a manner that each atom sees a “closed shell”. Since the donor atom introduces an additional electron, this electron is loosely bound; it is more free to move than the electrons which form the closed shell. This additional electron is easily put into the conduction band and can therefore conduct electricity easily. A donor-doped semiconductor is called an N-type semiconductor because it has negative charge carriers.
In other words, when a doping material is added, it gives away (donates) weakly-bound outer electrons to the semiconductor atoms. The purpose of N-type doping is to produce an abundance of mobile or “carrier” electrons in the material.
Monday, August 3, 2009
Semiconductors
Just for fun, today i will be doing something which i am interested in, which is semiconductors.
Semiconductors are actually solid crystalline substances of electrical conductivity between that of a conductor and an insulator.
Let me share with you what I have read. Electrons in semiconductors can have energies only within certain bands (i.e. ranges of levels of energy) between the energy of the ground state, corresponding to electrons tightly bound to the atomic nuclei of the material, and the free electron energy, which is the energy required for an electron to escape entirely from the material. The energy bands each correspond to a large number of discrete quantum states of the electrons, and most of the states with low energy (closer to the nucleus) are full, up to a particular band called the valence band. The ease with which electrons in a semiconductor can move from the valence band to the conduction band depends on the band gap.
Temperature affects the ease with which electrons move, which is why, the higher the temperature, the better the conductivity of a semiconductor.
Semiconductors are actually solid crystalline substances of electrical conductivity between that of a conductor and an insulator.
Let me share with you what I have read. Electrons in semiconductors can have energies only within certain bands (i.e. ranges of levels of energy) between the energy of the ground state, corresponding to electrons tightly bound to the atomic nuclei of the material, and the free electron energy, which is the energy required for an electron to escape entirely from the material. The energy bands each correspond to a large number of discrete quantum states of the electrons, and most of the states with low energy (closer to the nucleus) are full, up to a particular band called the valence band. The ease with which electrons in a semiconductor can move from the valence band to the conduction band depends on the band gap.
Temperature affects the ease with which electrons move, which is why, the higher the temperature, the better the conductivity of a semiconductor.
Saturday, August 1, 2009
Dynamics
Dynamics is the study of forces on an object.
The whole of the topic can be summarised into Newton's 3 laws.
1) An object at rest will remain at rest unless acted on by an unbalanced force. An object in motion continues in motion with the same speed and in the same direction unless acted upon by an unbalanced force.
2) Acceleration is produced when a force acts on a mass. The greater the mass (of the object being accelerated) the greater the amount of force needed (to accelerate the object).
This law is most famously represented by F=ma
3) For every action there is an equal and opposite re-action.
These can be used to solve many problems.
For example: a 2kg block requires 10N of force to move it at steady speed. What is its acceleration when 20N of force is applied on it?
F =ma, so the resultant force is 10N, since 10N of force is just requied to move it, and
20N - 10N = 10N.
Thus when we plug the numbers into the equation F = ma, we get: 10N = (2kg)(a)
thus the acceleration of the block when 20N of force is applied on it is 5 m/s^2.
The whole of the topic can be summarised into Newton's 3 laws.
1) An object at rest will remain at rest unless acted on by an unbalanced force. An object in motion continues in motion with the same speed and in the same direction unless acted upon by an unbalanced force.
2) Acceleration is produced when a force acts on a mass. The greater the mass (of the object being accelerated) the greater the amount of force needed (to accelerate the object).
This law is most famously represented by F=ma
3) For every action there is an equal and opposite re-action.
These can be used to solve many problems.
For example: a 2kg block requires 10N of force to move it at steady speed. What is its acceleration when 20N of force is applied on it?
F =ma, so the resultant force is 10N, since 10N of force is just requied to move it, and
20N - 10N = 10N.
Thus when we plug the numbers into the equation F = ma, we get: 10N = (2kg)(a)
thus the acceleration of the block when 20N of force is applied on it is 5 m/s^2.
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