Transcript Atomic Physics 4

IB Physics 12
Topic 13 – Waves vs. Particles
Mr. Jean
The plan:
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Video clip of the day
Millikan’s Spotting experiment
Wave Duality
De Broglie Wave Length
Compton Scattering
De Broglie Wavelength
• http://www.youtube.com/watch?v=lDYMuz
o40LU
Wave - Particle Duality of Light
• Modern age physics accepts that light
sometimes acts as a wave and at other
times acts like a particle.
• Both matter and electromagnetic energy
exhibit some properties of waves and
some properties of particles.
Wave Duality:
• Small Wave Length:
– Behaves like a particle.
• Large Wave Length:
– Behaves like a wave.
Compton scattering:
• This was the second big experiment which
proved that photons existed.
• It also had some interesting results.
With collisions we must consider:
• Conservation of Energy:
• Conservation of momentum:
Compton scattering:
• Major discovery supporting Quantum Theory
Compton Scattering:
• Compton scattering depends on how big
the wave is as it interacts with the
material’s surface in comparison to the
Compton wave length.
Compton Scattering
• http://www.youtube.com/watch?v=fI2C4VlR1OM
• http://www.youtube.com/watch?v=fI2C4VlR1OM
&list=PLFIIOUbmbUQI6vJD0kvxqcNoRAGXZ0dx
– This is a list of different videos explaining (some with
examples) of the Compton scattering model.
• The Problem:
– Electrons moving around a nucleus in roughly
circular or elliptical paths would feel a
centripetal force and would therefore have
centripetal acceleration.
– But accelerating charges produce electric
magnetic radiation, therefore these electrons
should continuously emit energy, slow down,
and eventually collapse into the nucleus.
– Obviously, this does not happen.
Bohr's Explanation:
• Laws of electromagnetism do not apply at
atomic level.
• Within an atom energy is only absorbed or
emitted when electrons change energy levels
and this energy is QUANTIZED.
• electrons are either in lowest energy state
(ground state) or certain allowed levels (excited
state).
• To move from one level to another,
electrons must emit or absorb a photon
with a certain amount of energy (E = hf).
• This absorbed or emitted photon had an
energy value equal to the difference
between energy levels.
Energy Levels:
• Bohr found that for the hydrogen atom, the
energy associated with a particular level was
given by:
• En = Energy from change (J)
• n = Quantum level
• Where n is principle quantum number (energy
level) and energy is negative because energy is
being added to pull the electron away from the
nucleus.
Changing Energy Levels
to Electrons:
• This is a great website highlighting states
of energy in matter.
• http://www.kcvs.ca/martin/astro/au/unit2/6
1/chp6_1.html
For the remainder of class:
• Review Topics
– SL  Review material on Topic #4
– HL
 Review