Saturday, 20 July 2013

Atoms and Radiations

This chapter deals with structure of atoms and radiations, If you are aware of Atoms and how radiations are produced, you may skip this chapter.

As you know anything that has mass and occupies space are called matters. Atoms are composed of fundamental particles called quarks and electrons. The quarks are held together by gluons which form Protons and Neutrons (Refer Particle Physics for more information). Both Protons and Neutrons are clustered in a small region called Nucleus. Electrons revolve around the nucleus in Orbitals and energy levels. There are certain energy levels present in an atom. As an electron gain energy it shifts from one energy level to another away from the nucleus and vice versa when it losses energy.

The following video would show you the various orbitals arrangement in an atom :

As already discussed charges in motion generate electrical and magnetic fields (Refer the four fundamental forces of nature). Since electrons are in motion they generate electrical and magnetic field called the electromagnetic fields. When photons are absorbed by the electrons, it moves to higher energy levels away from the nucleus. When a electrons are in motion they continue to loose energy in the form of electromagnetic radiations carried away by the photons (For more information about photons refer Particle Physics).

Watch this video for a brief account of how these radiations travel.

Electromagnetic radiations travel at a speed of 299,792,458 m/s. Radiation is energy in the form of waves. The wavelength of the radiations depend upon the velocity of the charged particles. Light, Particle ray, micro waves and radiation waves, X-rays are some example of electromagnetic radiation.

Wavelike behavior of Radiations : In most cases radiations behave like waves. The oscillating electrical and magnetic fiels are perpendicular to each other. Different frequencies of these waves give rise to different kind of electromagnetic Radiation.

Particle like behavior of radiations : In same cases radiations behave like particles. These particles include the Gauge bosons. For example, light radiation has photons. In fact these particles are the major energy carriers.

Photo Electric effects 

In 1887, H. Hertz performed a very interesting experiment. He connected metals to a electrical circuits and exposed high beam of light as shown in the picture. He observed that electrons were ejected which was verified by movements in Ammeter. The rate at which electrons were ejected was directly proportional to intensity of light.

Photoelectric effect

These results were explained by Einstein in 1905. A beam of light contains electromagnetic radiations. Photons are present in them which when fell on electrons provided energy to electrons to shift from lower energy levels to higher energy levels. As more energy is obtained by the electrons it it ejected out of the atom.Following the conservation of energy principle, the kinetic energy of the ejected electron is given by :

where m is the mass of electron and v is the velocity of the ejected electron, h is the plank's constant having the value of 6.626 x 10-34, hvo gives the minimum energy required to remove one electron.

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