1) Rutherford performed an experiment where he bombarded a thin gold foil with alpha particles and observed that most passed through without deflection, some were deflected by small angles, and a few were deflected back. 2) This led Rutherford to propose an atomic model where the atom has a small, dense nucleus containing its mass and positive charge, surrounded by electrons in orbits. 3) This was a major departure from the previous "plum pudding" model with a uniform distribution of charge. However, Rutherford's model failed to explain electron stability and other issues.

2. Rutherford Scattering & Scattering Cross-section
CLASSICAL MECHANICS
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3. Classical Mechanics
Submitted to : Ma’am Huma Malik
Submitted by : Group-5
B.S Physics (5th Semester)
Section (A)
GCWU Sialkot

4. Group Members:
 Bisma Shakir 14020210-
018
 Maria Kousar 14020210-
005
 Ishrat Fardoos 14020210-
012
 Warda Jabbar 14020210-
048
 Fauzia Tehleel 14020210-
033
Classical Mechanics
 Faiqa Barkat 14020210-
027
 Nimra Asmat 14020210-
021
 Maham Idress 14020210-
010
 Rida Bukhari 14020210-
028

5. Layout Of Presentation:
Rutherford Scattering Experiment
Theory of α–Particle Scattering
Scattering via the Coulomb force
Geiger-Marsden Experiment
The impact parameter/scattering angle relationship
1- Linear Momentum 2- Angular momentum
The Cross-Section
How Rutherford’s Atomic Model is Different From Thomson Atomic M
odel???
Drawbacks of Rutherford Model
Bibliography

6. Rutherford’s Scattering Experiment:
 Rutherford in 1911 , performed some scattering experiments in
which he bombarded thin foil of gold with a beam of fast moving
alpha particles.
 The thin gold foil had a circular fluoriscent zinc sulphide screen
arround it.
 Whenever , alpha particles struck the screen , a tiny flash was
produced at that point.
From these experiments , he made the following observations :
1. Most of the alpha particles passed through the foil without
undergoing any deflection.
2. A few alpha particles underwent deflection through small angles.
3. Very few mere deflected back i.e., through an angle of nearly 180⁰.

8. Alpha particles
hit atoms with
massive
nucleus cores.
Continue…

9. Theory of α–Particle Scattering:
 Assuming α-particles and nucleus are point charges.
 Impact Parameter “b” is the minimum distance to which
α-particle would
approach the nucleus if there is no force between them.
 b = 0 for head collision.
 Distance of closest approach “D” is the minimum distance
to which particle approaches nucleus head on.
 Scattering angle “θ” is the angle between the asymptotic
direction of approach of α-particle and the asymptotic
direction in which it recedes.
 Trajectories are hyperbolic.

10. Continue…

11. Scattering via the Coulomb force:
Charged-particle induced reactions:

12. Continue…
Trajectories in Rutherford Scattering:

13. Continue…
Trajectories in Rutherford Scattering:

14. Geiger-Marsden Experiment:

15. Geiger-Marsden Experiment:
The ironic ways of nature:

16. Geiger-Marsden Experiment:

17. The impact parameter/scattering
angle relationship:

18. The impact parameter/scattering
angle relationship:

19. The impact parameter/scattering
angle relationship:
Momentum change in Rutherford scattering:

20. The impact parameter/scattering
angle relationship:
The momentum change:

21. The impact parameter/scattering
angle relationship:
Trajectories in Rutherford Scattering:

22. The impact parameter/scattering
angle relationship:
The momentum change:

23. The impact parameter/scattering
angle relationship:
The angular momentum:

24. The impact parameter/scattering
angle relationship:
The angular momentum:

25. The impact parameter/scattering
angle relationship:
Conservation of angular momentum:

26. The impact parameter/scattering
angle relationship:
Integration limits:

27. The impact parameter/scattering
angle relationship:

28. The impact parameter/scattering
angle relationship:
The distance of the closest approach:

29. The Cross-Section:
The cross section in Rutherford Scattering :

30. The Cross-Section:

31. The Cross-Section:
Cross-section in Rutherford Scattering:

32. How Rutherford’s Atomic Model
is Different From Thomson
Atomic Model????
 Rutherford proposed a model in which electrons revolve around the
nucleus in well-defined orbits.
 There is a positively charged centre in
an atom called the Nucleus.
 He also proposed that the size of the
nucleus is very small as compared to
size of the atom and nearly all the
mass of an atom is centered in the
nucleus.

33. How Rutherford’s Atomic Model
is Different From Thomson
Atomic Model????
Thomson proposed the model
of an atom to be similar to a
christmas pudding.
The electrons are in positively
charged sphere like christmas
pudding and the mass of the
atom was supposed to be
uniformly disturbed.

34. Drawbacks of Rutherford Model:
The Rutherford’s atomic model explains the structure of an
atom in a very simple way. But , it suffers from the following dra
wbacks:
 Rutherford stated that electrons orbits the nucleus.Thus, if
the electrons were orbiting the nucleus then they must be
accelerating due to the centripetal force acting on it.
 This proved to be a flaw, due to Maxwell theory that
electrons accelerating produces EMR which in turns would
mean the electrons would loose energy and crash into the
nucleus leading to a unstable atom. Which is not the case.
 The Rutherford’s model of atom does not say anything
about the arrangement of electrons in an atom.

35. Bibliography:
 http://www.slideshare.net/deepak190/rutherford-s-model-of-an-
atom
http://www.sjsu.edu/faculty/watkins/scattering.htm
 http://diablo.phys.northwestern.edu/~mvelasco/591-596.pdf
http://www.answers.com/Q/What_is_the_major_flaw_of_Rutherf
ord's_model?#slide=3
 http://www.slideshare.net/RohitKumarShah1/rutherford-gold-foi
l-experiment
http://www.preservearticles.com/201012302032/drawbacks-in-th
e-rutherfords-nuclear-model-of-an-atom.html