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

fhnE

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 voltageCurrent increases with intensity Threshold is a function of light

frequencyNo intensity thresholdNo time delayFairly 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. Infra-redB. VisibleC. Ultra-violet

What is the velocity of the electrons coming off the

metal?

22

1mv hf

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. More electrons are emitted in a given

time interval.B. The electrons that are emitted are

more energetic.C. Both of the aboveD. 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. More electrons are emitted in a given

time interval.B. The electrons that are emitted are

more energetic.C. Both of the aboveD. 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. Yes, it acquires a positive charge.B. Yes, it acquires a negative charge.C. No, it does not acquire a charge.

Double Slit Interference

Single Photon Interference

X-Ray Tube

-+

CathodeAnode

-FilamentTungsten

Target

)cos1( cm

h

eif

In the Compton experiment, the wavelength of the scattered light is ______________ the wavelength of the incident light.

A. Longer thanB. The same asC. Shorter than

Compton Scattering of a “Photon”

e-

Before

e-

After

Are you pondering whatI’m pondering?

Yes, but how will we ever get that many rubber bands?

No you buffoon! Why do youneed x-rays to see this?