write the main reason for downfall of thomsons model of an atom ?
Asked by | 27th Mar, 2009, 10:16: AM
Now we prove that why thomson's model cannot be held true. We can consider that
the scattering angle
of the alpha particle
by Thomson's model
is at most 0.01 degrees.
The thickness of
the metal foil
in the scattering experiment
of the alpha rays
is about 10-6 m.
When assuming
that the atoms are
tightly packed
in the metal,
there are about 10000 atoms
lining up
in the direction
of thickness,
because the size
of an atom is
approximately 10-10m.
(See the following figure.)
When the alpha particle
collides with these atoms
in the metal foil
10000 times successively,
the scattering angle
of each individual collision
in such a multiple scattering
is less than 0.01 degrees
as discussed above.
The resultant scattering angle
is obtained
by an accumulation of
these individual scatterings
of 10000 times.
One may expect that,
even if the scattering angle
of each individual scattering
is very small like 0.01 degrees,
we can have
as large resultant angle
as
This is however
unrealistic,
because the direction
of each individual scattering
must be random,
and an accumulation
of random values would give
nearly zero only.
So that we never obtain
such a large resultant scattering
angle after the multiple
scattering.
Accordingly,
such a large scattering angle
as those obtained
in Geiger and Marsden's experiment
cannot be reproduced
by such a multiple
scattering as stated above.
Thus we can conclude that
Thomson's atomic model
is not held.
Answered by | 27th Mar, 2009, 11:19: AM
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