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Pre-Quantum
Theory
Maxwell
• A change in a electric field produced a
magnetic field
• A change in a magnetic field produced
an electric field
Light Transmission
• Light propagated as a wave.
Older Wave Theory:
• Some things are unexplainable with
older wave theory:
• 1. Wave theory could not explain
why a hot body emitted light.
• 2. UV-light discharged electricallycharged metal plates (the
photoelectric effect).
Quantum Theory
Max Planck
• The energy of vibration of the
atoms in a solid could have only
specific frequencies
Max Planck
• E = nhf
• f=frequency of vibration
• h=constant {7 x 10-34 J/Hz}
• n=integer (0,1,2,3,etc.)
Max Planck
• This is said to be quantized energy.
• Electrons are emitted from a negatively
charged metal plate with a potential
difference when UV-light falls on it.
• A) Only radiation above the threshold
frequency (f0)ejects electrons no matter
what intensity the light.
• B) Photon- electromagnetic radiation
travels in packets with a given amount
of energy based on the frequency of the
radiation. [Einstein]
• E = hf
• EM radiation has properties of particles.
• KE = hf - hfo
• Think conservation of energy.
• This is going to be KEmax of an electron
since hfo is the minimum energy needed
to free an electron (assuming it is
freeing a higher energy electron).
• hf0 is the energy needed to free the
electron and will not accumulate.
• One photon interacts with one electron.
• A known frequency of X-ray were
directed at a graphite block, some
scattered X-rays were found to have
lower frequencies (increased
wavelength).
• Therefore, they lost energy &
momentum in collisions.
Louis Victor de Broglie
• materials have wave properties
•
l
=
h
=
h
mv
p
• Beams of electrons shot through a
crystal showed diffraction grating
patterns similar to those of X-rays with
similar wavelength.
•Particle
• located at one point in
space
•Wave
• continuous space needed
to make a wave
• can not travel through solid • can travel through solid
objects (cannot occupy
objects
same space at same time)
• can occupy same space at
the same time with losing
energy
• have mass, size, KE, &
momentum
• frequency, wavelength,
amplitude
• Beams of electrons shot through a
crystal showed diffraction grating
patterns similar to those of X-rays with
similar wavelength.