Science - Teachers Sri Lanka

Copyright © 2007 National Institute of Education - Sri Lanka. All rights reserved.
J.J.Thompson conducted an experiment to determine the (e/m ) ratio of the cathode ray
particales, where (e) is the charge and (m) is the mass.
The value he got for e/m was very large
e/m=1.76x10 c kg -1
The values obtained for e/m ratio for the cathode rays using different gases and different cathodes
is the same.By this Thompson concluded that the cathode rays consists of the same
particles.Further Thompson stated that,the fundamental unit of electricity,the electron introduced
by J.J. Stony in 1874 B.C.is the negatively charge particles in the cathode rays.
Electron is a common sub atomic particle present in all atoms.
Charge of an electron = 1.602x10 -19 C
Mass of an electron = 9.1095x10 -31 kg
At present different forms of cathode ray tubes are used in various electronic instruments.
Some of these are TV photo tube,Computer monitor,Cathode ray Oscilloscope,
Fluorescent tube
Proton
Cathode
High Voltage
To Vaccum Pump
Simple Cathode Ray Emitting Tube
Anode
In 1886 B.C. E.Goldstien observed that when using a porous Cathode,is subjected to a voltage
from 20,000V to 50,000V some special rays were seen to emit from the pores in the Cathode in
a direction opposite to the Cathode rays.He named them as positive rays.
When ratio e/m was calculated for the particles in these positive rays it was found that the value
is numerically smaller to that of the particles in the cathode rays.
When different gases were used in the Cathode ray tube the e/m ratio for the particles in the
possitive rays were found to be whole numerical multiples of the e/m ratio for the particles in the
possitive rays.When Hydrogen gas is used in the cathode ray tube.In short the lightest possitive
rays particles were obtained from Hydrogen.In 1871 B.C-!937B.C Rutherford,named this lightest
possitive ray particle as proton and also that it should be the common possitively charged fundamental
particle of all matter.
Charge of a proton=1.602x10-19C
Mass of a proton=1.6726x10-27 Kg
Mass of a proton is 1840 times the mass of an electron.
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