PARTICLE
1. A particle occupies a well-defined position in space i.e a particle is localized in space e.g. a grain of sand, a cricket ball etc.
2. When a particular space is occupied by one particle, the same space cannot be occupied simultaneously
by any other particle. In other words, particles do not interfere.
3. When a number of particles are present in a given region of space, their total value is equal to their sum, i.e. it is neither less nor more.
WAVE
1. a wave is spread out in space, e.g. on throwing a stone in a pond of water, the waves start moving out in the form of concentric circles. Similarly, the sound of the speaker reaches everybody in the audience. Thus, a wave is delocalized in space.
2. Two or more waves can coexist in the same region of space and hence interfere.
3. When a number of waves are present in a given region of space, due to interference, the resultant wave can be larger or smaller than the individual waves i.e. interference may be constructive or destructive.
Experiments to prove particle and wave property of Electrons
a) Verification of Wave character
i) Davis son and Gerber Experiment
In 1927 Davis son and Gerber observed that, a beam of electrons obtained from a heated tungsten filament is accelerated by using a high positive potential. When this fine beam of accelerated electron is allowed to fall on a large single crystal of nickel, the electrons are scattered from the crystal in different directions. The diffraction pattern so obtained is similar to the diffraction pattern obtained by Bragg’s experiment on diffraction of X-rays from a target in the same way
Fig.1.1 Electron diffraction experiment by Davis son and Gerber Since X-rays have wave character, therefore, the electrons must also have wave character associated with them. Moreover, the wave length of the electrons
as determined by the diffraction experiments were found to be in agreement with the values calculated from Brollies equation. From the above discussion, it is clear that an electron behaves as a wave.
ii) Thomson experiment
G.P. Thomson in 1928 performed experiments with, thin foil of gold in place of nickel crystal. He observed that if the beam of electrons after passing through the thin foil of gold is received on the photographic plate placed perpendicular to the direction of the beam, a diffraction pattern is observed as before.
This again confirmed the wave nature of electrons.
1.2 Diffraction of electron beam by thin foil of gold (G.P. Thomson
experiment)
b) Verification of the particle character The particle character of the electron is proved by the following different experiments:-
i) When an electron strikes a zinc sulphide screen, a spot of light known as scintillation is produced. A scintillation is localized on the zinc sulphide screen.
Therefore, the striking electron which produces it, also must be localized and is not spread out on the screen. But the localized character is possessed
by particles. Hence, electron has particle character.
ii) Experiments such as J.J. Thomson experiment for determination of the ratio of charge to mass (i.e. e/m) and Mil liken oil drop experiment for
determination of charge on electron also show that electron has particle character.
iii) The phenomenon of Black body radiation and Photoelectric effect also prove the particle nature of radiation.
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