Radioactivity

   
(Discivered by Henry Becquerel in 1836 and named by Marie Curie):-

Definition:-
Phenomenon of spontaneous emission of radiation through the nuclei of certain elements like Uranium is called Radio activity.
Explanation:-
It is found that nuclei of some elements like uranium have property to emit radiations or rays spontaneously. This property of an element is called radio activity, and the element is called radio active element, while the rays are called radio active rays. Radio active rays are invisible,  and by the emission of these rays nuclei of one element change to the nuclei of another element. All the elements above lead Pb (82) are naturally radio active elements.

Types Of Radio Active Rays:-
Rutherford found that there are three types of radio active rays.
Alpha rays
Beta rays
Gamma rays.

Properties of these rays are given below:

1) Properties of Alpha Rays:-
 Alpha rays have following properties.
• alpha rays are double positive charged particle with 4 a.m.u mass. Thus they contain two protons and two neutrons and are called Helium nuclei.
• alpha rays are heavy particles due to high mass.
• Magnitude of charge of each alpha particle is 3.2*10^-19 coulombs.
• alpha rays travel with the velocity 10 times less than the velocity of light.
• alpha rays can be deflected in the electric and magnetic field toward negative plate.
• alpha rays produce fluorescence on the fluorescent screen and also affect the photographic film.
• alpha rays have very low penetration powers and can penetrate through a paper and up to few centimeters in air.
• alpha rays are best ionizer of gasses. They ionize gasses (eject electrons)  with which they strike.

2) Properties of Beta Rays:-
  Beta rays have following properties.
• Beta rays are negative charged particle.
• Beta rays have e/m ratio of electron. Thus they contain electrons.
• Mass of beta particles is 9.11*10^-28 g.  Thus they are very light particles.
• beta rays have velocity more than alpha rays.
• beta rays have high penetrating power than alpha rays.
• beta rays are weak ionizer of gasses
• beta rays can be deflect in electric and magnetic field toward positivr pole.
• beta rays also affect the photographic film.


3) Properties of Gamma Rays:-
  Gamma rays have following properties.
• gamma rays have no charge
• gamma rays are non material in nature mean they have no particle.
• gamma rays are only the waves of energy with wave lenght shorter than X-rays
• gamma rays have velocity of light.
• gamma rays have very penetrating powers.
• gamma rays also affect the photographic film.
• gamma rays are weak ionizer of gasses due to non material nature.

Spectrum OR Spectra:-

Definition:-
When tha radiation is passed through a prism it split into a band of rays with different wave lenghts. This band of rays is called spectrum.

Explanation:-
Ordinary light is composed of rays of different wave lenghts. These rays are combine with each other and we can not see them separate,  but when this light is passed through a prism then different rays in it deflect at different angles and become separate in the form of a band of ray are called spectrum. If the rays are of visible light then spectrum is obtained as a band of colours.

Types of Spectrum:-
There are two types of spectrum.
Continous spectrum
Line spectru
1) Continous spectrum:-

 Definition:-
 Band of seven colour obtained by passing ordinary sun light or bulb light through a prism is called continous spectrum.

Explanation:-
Ordinary light like sun light or bulb light is composed of seven types of rays having different wave lenghts. These rays also have different colours. When this light is passed through a prism then the rays deflect at different angles and can be seen in the form of a band of seven colours this is known as continous spectrum because these colours are continous to each other. Thus the seven colours of spectrum represent the seven types of rays.

Colours of Spectrum:-
• Violet
• Indigo
• Blue
• Green
• Yellow
• orange
• red.
(VIBGYOR)

Wave lenght of rays
400nm to 4000 Angstrom to
750nm to 7000 Angstrom.
Violet rays have the shortest wave lenght and deflect at the highest angle while red rays have longest wave lenght and deflect at lowest angle.

Dark Space

2)Line Spectrum:-

Definition:-
Spectrum in which colour line are separated by dark space is called line spectrum.

Explanation:-
Line spectrum is given by elements and compounds. When light is emitted by burning of an element or a compoumd is passed through a prism, it gives coloured lines separated by dark space. Coloured lines are the waves of light with a definite wave lenght. Each element gives its own coloured lines, thus the line spectrum is used to identify the elements.

Bohr's Theory and Hydrogen Atom:-
(Calculation of radius of Hydrogen atom)
Hydrogen has one electron which revolves in its first orbit around the nucleus.
Nucleus of hydrogen contain one proton.
n = no: of orbit
r = radius of orbit
e = charge of electron
m = mass of electron
Ze = charge of nucleus in which Z is the no: of proton.

Two forces on electron
Centripetal force
Centrifugal force.