# 15 01 2013 Physics 12 Wave Duality and Atomic Theory

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```					 Physics 12

Mr. Jean
January 11th, 2012
The plan:
•   Video clip of the day.
•   Collecting visiting the relatives
•   Upcoming Assignments
•   Planck’s Constant
•   Wave Duality
•   Atomic Theory
Planck’s Constant:
PrQs
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:
• Major discovery supporting Quantum Theory
Compton Scattering
• http://www.brightstorm.com/science/physic
s/the-atom-and-quantum-
physics/compton-scattering/

R1OM
Bohr Model:
• Bohr model, emission spectra, energy
levels problem:
– only 4 visible lines appeared when hydrogen
atoms were energized.

• PHYSICS 123 Demonstration: 9.1

• How do we explain this as a model for an
atom?
• 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
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:
• 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:
• http://www.kcvs.ca/martin/astro/au/unit2/6
1/chp6_1.html

```
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