Transcript Bohr´s Third Postulate

Bohr’s Third Postulate
A single photon is emitted whenever an
electron jumps down from one orbit to
another.
hf  Eupper  Elower
1. Why do astronomers often use the terms color and
temperature interchangeably when referring to stars?
2. Why did Bohr assume that the electrons do not radiate when
they are in the allowed orbits?
Wave Nature of Matter
De Broglie Wavelength
h

mv
Wave-particle duality apply also to
matter.
De Broglie’s Hypothesis Applied
to Atoms
Quantum Mechanics of Atoms
The Wave Function and Its
Interpolation
In quantum mechanics the amplitude of a
particle wave is called the wave function and is
given the symbol Y.
If we are dealing only with one photon:
At any point the square of the electric field
strength is a measure of the probability that
a photon will be at that location.
For a single particle:
Y2 at a certain point in space and time
represents the probability of finding the
electron at the given position and time.
Important: there is no way to predict
where one electron would hit the screen.
We could predict only probabilities.
The main point of this discussion is
this: if we treat electrons as if they were
waves, then Y represents the wave
amplitude. If we treat them as particles,
then we must treat them on
probabilistic basis.
The Heisenberg Uncertainty
Principle
The act of observing produces a significant
uncertainty in either the position or the
momentum of electron.
h
xp 

2
34
  1.06  10 J  s
Position uncertainty of a baseball
What is the uncertainty in position, imposed by the uncertainty
principle, of a 150-g baseball thrown at 42+-1 m/s? Should the
umpire be concerned? Can he use Heisenberg as an excuse?
Particle in a Box
Baby-Quiz
1. If all objects emit radiation, why don’t we see most of them in the
dark?
2. Suppose you were a nineteenth-century scientist who had just
discovered a new phenomenon known as Zeta rays. What experiment
could you perform to define if Zeta rays are charged particles or e/m
waves? Could this experiment distinguish between neutral particles
and an e/m wave?
3. If a metal surface is illuminated by light at a single frequency, why
don’t all the photoelectrons have the same kinetic energy when they
leave the metal’s surface?
4. What property of the emitted electrons depends on the intensity of
incident light?What property of the emitted photoelectrons depends
on the frequency of incident light?