CHARLES AUGUSTIN de COULOMB

French  physicist, best known as for the formulation of Coulomb's law, Which states  that the force between two electrical charges is proportional to the product of the charges and inversely proportional to the square of the distance between them. Coulombic force is one of the principle forces involved in atomic interactions.

Coulomb developed his law as an outgrowth of his attempt to investigate the law of electrical repulsions  as stated by Joseph Priestly of England. To this end he invented sensitive apparatus to measure the electrical forces involved in Priestly's law and published his findings in 1785-89. He also established the inverse square law of attraction and repulsion of unlike and like magnetic poles, which become the basis for the mathematical theory of magnetic forces developed by Simeon- Denis Poission. The coulomb, a unit of electric charge, was named after Coulomb in his honour.

SURFACE ENERGY OF LIQUID

The molecules of a liquid are in a state of random motion inside the liquid. A molecule is attracted by other molecules lying within a range of  molecular force. A sphere of radius equal to the range of molecular force is called Sphere of molecular influence. The molecule at the centre of molecular influence is attracted equally in all the directions by all other molecules in the sphere.


For a molecule A, well inside the liquid, the forces of attraction on the molecule are equal in all directions. Hence net force on it is zero. consider a molecule B near the surface. In this case the sphere of molecular influence is partially outside the liquid. But the molecules within the liquid lying in the molecular influence attract the molecule B. So there is a net downward force.

Consider another molecule C on the surface of liquid. Half of the sphere of influence is outside the liquid. Hence the downward force on molecule is maximum. Thus when a molecule comes to the surface , it is doing work to over come this downward pull. The work done resides as potential energy in the molecule on the surface.

Thus  molecules on the surface of liquid have  potential energy. This energy is called the surface energy. To increase the area of a liquid, work has to be done. Thus energy is required to increase the surface area. The energy required to increase unit area of the surface is called the surface energy.

KEPLER'S LAWS OF PLANETARY MOTION

In 1543 Nicolaus Copernicus stated that all planets move around the sun in circular orbits with the sun at the center. But Johannes Kepler (1571-1630) discarded this theory and proposed the elliptical orbits for the planetary motion. he formulated three laws known as Kepler's law of planetary motion.




1)  KEPLER'S FIRST LAW (LAW OF ELLIPTICAL ORBIT)

       Every planet revolves round the sun in elliptical orbits, with the sun at one of the foci.     




2)   KEPLER'S SECOND  LAW ( LAW OD EQUAL AREA)

       The line joining the sun and the planet sweeps out equal areas in equal intervals of time.  i.e., the areal velocity swept by the radius vector of ellipse is a constant.




3)   KEPLER'S THIRD LAW ( HARMONIC LAW)

      The square of the time period of the revolution of planet around the sun is directly proportional to the cube of the mean distance between the sun and planet.

FORCE AND MOTION

Forces are pushes or pulls that change the motion of objects. To make a stationary object move, or a moving object stop, a force is needed. A force is also required to change the speed or direction of an object. This change in speed or direction is known as acceleration. Acceleration depends on the size (magnitude) of the force and on the mass of the object. The effects of forces were first summarized by Isaac Newton in his three laws of motion. the international unit of force, named after him, is known as newton (N), which is approximately equal to the weight of one apple. Gravity-the force attraction between any two masses can be measured using newton meter (spring balance). Forces are put to useful effect in machines. A simple machine, such as a wheel and axle, is a device that changes the size or direction of an applied force. It allows an applied force (the effort) to produce another force (the load). A lever uses a bar that turns on a fulcrum to exert force. In all simple machines, there is a relationship between force and distance. A small force (in a compound pulley, for instance) moves through a large distance to lift a heavy object a small distance. This is called the Law of simple Machines.

VAN DE GRAAFF GENERATOR, ITS PRINCIPLE,CONSTRUCTION AND WORKING.

V a N      d E     G r A a F f     G E n E r a T O r

A Van de Graaff  generator is a device designed to create static electricity and make it available for experimentation.
  
                      The American physicist Dr. Robert Jemison Van de Graaff invented the Van de Graaff generator in 1931. The device
has the ability produce extremely high voltages as high as 20 million volts. Van de Graaff invented the generator to supply the high energy needed  for early particle accelerators. these accelerators are known as atom smashers because they accelerate the sub-atomic particles to very high speeds and then "smashed" them into the target atoms. The resulting collisions created other subatomic particles and high energy radiation such as X-rays. The ability to create these high-energy collisions in the foundation of particle and nuclear physics.


PRINCIPLE:

The Van de Graaff generator works on the following two principles.

1. Discharging action of sharp points i.e., electric discharge takes place in air or gases readily at pointed conductors.
2. If the charged conductor is brought into internal contact with a hollow conductor , all of its charge transfers to the surface of the hollow conductor  no matter how high the potential of the latter may be.

CONSTRUCTION:

M- a large spherical conducting shell is supported at a height several meters from the ground on an insulator column.

B- an insulating belt wound around two pulleys P1 and P2, this belt is moving continuously by a driven motor at constant speed.

C1,C2- sharply pointed combs close to the belt near its bottom and top, C1 has given 10kV by a high-tension battery (HT) and termed as spray comb and C2 is connected to spherical shell and termed as collector comb.

WORKING:

The high electric field at the pointed end comb C1 ionises the air near them. The +ve charges in air are repelled and got deposited on the belt through a corona discharge. The charges are carried upto C2. A similar corona discharge takes place at C2 and the charges are finally transferred to the shell M. The charge spread over uniformly on the outer surface of M raising its potential to few million volts.

FTP (File Transfer Protocol) AND IT'S ADVANTAGES

FTP is a convention or set of rules used for transferring files from one computer (or network) to another computer (or network). Thus FTP allows copying of files from a remote server to our own computer and transferring files from our computer to some remote computer. Using FTP a user can log on to a remote computer by giving the address of the host computer.

Besides managing the access control and file transfers, FTP also deals with protection given to a file. Protection may not be given to a file if it is assumed that all the clients are trustworthy. Whenever the clients make requests, the server provides the requested files as they are.

A second alternative is to assign a password to each authorized user. The server, before giving access to any file, will check the password of the client and process his/her request only if the password is valid. A third alternative is assign a password to the files. The passwords assigned for files provide different access rights such as read only, modification and full control.


ADVANTAGES OF FTP :

• Useful for transferring files from one network in an organization to another.
• Geographically separated groups working on a common project may co-operate and co-ordinate with each other.
• Most useful way of sharing information and resources over WANs like internet.

 

URL (Universal Resource Locator)

The function of the web server hardware and software is to store the web pages and locate and transmit them to a client computer as and when requests for the web pages come in. When we want to download a website, its address is to be specified at the concerned prompt in the browser program. the web site address is called Universal Resource Locator (URL), which is the address of the home page of the website installed on the web server. There is standard format for the web sited address. It has generally  three parts (eg  www.abcd.com) where www is based on the HTTP, the recent addition to the TCP/IP protocol suite; abcd represents the name of the site; and com is the domain name that describes organizational or geographical realities like com, org,  in, au, etc