11.1 INTRODUCTION -

In 1887, Hertz experiment on the generation and detection of electromagnetic wave and the maxwell equation of electromagnetism strongly established the wave nature of light.

At the same period, the discharge tube experiment led to many historic discoveries.

ELECTRIC DISCHARGE THROUGH GASES AT LOW PRESSURE

(Please, students understand this experiment well with their teacher.)

It is found that at the very high potential difference and at a very low pressure of the gas (0.001 mm of HG). A fluorescent glow appeared on the discharge tube. This fluorescent glow appeared on the glass when cathode ray particles are striking on the glass.

* The colour of glow of the glass depended on the type of the glass, it being yellowish-green for soda glass.

* These cathode rays were discovered in 1870.

* In 1879, crooks suggested that these rays consisted of streams of fast-moving negative charge particles and later J.J Thomson confirmed this hypothesis by various experiments.

* Thomson was the first to determine experimentally the specific charge (e/m) of the cathode ray particle by using perpendicular electric and magnetic fields across the discharge tube.

$\fn_jvn evB=eE\$

where v is the velocity of cathode ray particles

$\fn_jvn \left [ v=\frac{E}{B} \right ]$

we know that $\fn_jvn \frac{1}{2}mv^2=eV$

Where V is the potential difference between cathode and anode

$\fn_jvn \frac{1}{2}m\frac{E^2}{B^2}=eV$

$\fn_jvn \left [ \frac{e}{m}=\frac{E^2}{2B^2V} \right ]$

$\fn_jvn \left [ \frac{e}{m}=1.76\times10^{11} C/kg \right ]$

This value is independent of the nature of the material used in the cathode or the gas

* He also determined the speed of cathode ray particles and found that it is to be travel ranging from about (0.1 to 0.2 times) the speed of light $\fn_jvn 3\times 10^{8}m/s$

Around the same period

It was found that certain metals, emitted negatively charged particles when irradiated by UV light.

Certain metal is also emitted negatively charged particles when heated to high temperatures.

The value of (e/m) of these particles are the same as for cathode ray particles.

In (1897) J.J. Thomsom named these particles as electrons and suggested that they were fundamental universal constituents of matter.

in 1895, X rays were also discovered by Roentgen.

* In 1913, the Americal Physicist R.A. Mullikan perform the oil drop experiment for the measurement of the charge on an electron.

$\fn_jvn e=1.602\times10^{-19}\;C$ ( and this electric charge is quantized)

and mass is also calculated by (e/m)

$\fn_jvn m=9.11\times10^{-31}\;kg$

IMPORTANT LINKS OF DUAL NATURE OF RADIATION AND MATTER
Introduction	Electron Emission
Photoelectric Effect	Experimental Study of Photoelectric Effect
Photoelectric Effect and Wave Theory of Light	Einstein’s Photoelectric Equation: Energy Quantum of Radiation
Particle Nature of Light: The Photon	Wave Nature of Matter
Davisson and Germer Experiment