### Atomic  Theory of matter :-

According to this theory , atom is the ultimate particle of matter , also known as Dalton’s  Atomic theory (1808).

#### Cathode ray discharge tube experiments: -

1.     Cathode rays start from cathode and move toward anode.
2.     These rays are not visible but there behaviour can be observed with fluorescent or phosphorus sent material.
3.     In the absence of magnetic or electric field these travels in strait lines
4.     In the presence or magnetic or electric field the behaviour of cathode rays in similar TO Negatively  charged  particles  which suggest that these rays contain negatively charge particles called electron
5.     Cathode rays (electrons) do not depend on  the martial of the electrode and  nature of the gas tin the tube so electro us are basic constituent of all atoms.

#### Charge (e) to mass (me) ratio of electron

ð Measured by  J. J. Thomson (1897).
ð By using cathode ray tube ; applying electrical & magnetic field perpendicular to each other also perpendicular to path of electrons.
ð He proposed  deviation of particles from their path in presence of magnetic or electrical field depend upon the following
1.     Magnetic of  – ve  charge on particle
i.e. it magnitude of charge on particles is greater than interaction with magnetic or electric field is greater so deflection is also grater.
2.      Mass of particles
i.e. particle is lighter then deflection is greater.
3.  Strength of magnetic or electric field.
i.e. it strength of magnetic  field or voltage at electron is increases then deflection of                                            e-  also increases
=>  value of e/me = 1.758820× 1011 C kg-1

#### Charge of electron

=>  Determine by  R. A. Millikan
=>  By oil drop experiment (1906-1914)
=>  Charge on e- =  -1.6× 10-19 C
=> Present accepted value , e- = -1.6022× 10-19 C

#### Mass of electron

From charge on e- & e/me
We get,
Me = 9.1094 ´ 10-31 kg