Blackbody Radiation
Max Planck, Planck’s constant
Max Karl Ernst Ludwig Planck

Found an empirical
formula which fit the
measured blackbody
curve

Looked for way to
derive this empirical
formula
Photo from http://www-groups.dcs.st-and.ac.uk/~history/PictDisplay/Planck.html
Max Planck, Planck’s constant
E  n  fh
Max Karl Ernst Ludwig Planck
Photo from http://www-groups.dcs.st-and.ac.uk/~history/PictDisplay/Planck.html
Disclaimer . . .
What did Einstein Win his Nobel
Prize for?
photo from http://www.th.physik.uni-frankfurt.de/~jr/gif/phys/einst_7.jpg
The Photoelectric Effect
Photoelectric Effect Intuition

What would a plot of current vs. light
intensity look like?

What would a plot of current vs. voltage
look like?

What would a plot of threshold voltage vs.
light frequency look like?
WHAT BROUGHT DOWN THE
NEPHITES
200 years of peace after Christ's visit.
 Began to be Lamanites
 Costly Apparel
 Churches built to get gain
 Persecuted prophets who were doing
miracles
 Willful rejection of good
The Photoelectric Effect
The Photoelectric Effect
Wave Theory of Light and the
Photoelectric Effect
Existence of a threshold voltage
Current increases with intensity
Threshold is a function of light frequency
No intensity threshold
No time delay
Fairly monochromatic electron energies
Einstein’s Explanation...
Plank was right!
photo from http://www.th.physik.uni-frankfurt.de/~jr/gif/phys/einst_7.jpg
Photons and Work Functions
Light is incident on a Zinc plate (Φ=4.31 eV).
Only one of the following lights will cause
the electrons to be emitted from the surface,
which one is it.
A.
B.
C.
Infra-red
Visible
Ultra-violet
What is the velocity of the
electrons coming off the metal?
1
2
mv  hf  
2
A beam of ultra violet light is incident on the
metal ball of an electroscope (hf > Φ) that is
initially negatively charged. The electroscope
...
Losses its negative
charge.
A beam of visible light is incident on the
metal ball of an electroscope (hf < Φ)
that is initially negatively charged. The
electroscope . .
Nothing happens—
even after a long
time.
Why does UV light give you a
sunburn?
Discussion question: 400-nm wavelength light
strikes a metal surface, a stream of electrons
emerges from the metal. If the intensity of the
light striking the surface is doubled,
A.
B.
C.
D.
More electrons are emitted in a given time
interval.
The electrons that are emitted are more
energetic.
Both of the above
Neither of the above
Discussion question: When 400-nm wavelength light
strikes a metal surface, a stream of electrons emerges
from the metal. If the 400-nm light is replaced with
300 nm and the lamp is adjusted so that the intensity
of the light striking the surface is the same as it was
for the 400-nm light. With the 300-nm light,
A.
B.
C.
D.
More electrons are emitted in a given time
interval.
The electrons that are emitted are more
energetic.
Both of the above
Neither of the above
Discussion question: A beam of ultra-violet
light is incident on the metal ball of an
electroscope that is initially uncharged. Does
the electroscope acquire a charge?
A.
B.
C.
Yes, it acquires a positive charge.
Yes, it acquires a negative charge.
No, it does not acquire a charge.
Double Slit Interference
Single Photon Interference
X-Ray Tube
+
Tungsten
Target
Anode
-
Filament
Cathode
h
 f  i 
(1  cos  )
me c
In the Compton experiment, the wavelength
of the scattered light is ______________ the
wavelength of the incident light.
A.
B.
C.
Longer than
The same as
Shorter than
Compton Scattering of a “Photon”
Before
After
ee-
Are you pondering what
I’m pondering?
Yes, but how will we ever get that
many rubber bands?
No you buffoon! Why do you
need x-rays to see this?