EM Spectrum, de Broglie, PE Notes

de Broglie Wavelength

de Broglie• Pictured the electron in its circular orbit as a

particle wave

• Can produce "standing waves" under resonant conditions

• Developed the idea that a particle with mass, m, and a velocity, v, has a wavelength associated with it => de Broglie Wavelength

de Broglie

de Broglie

de Broglie

Schrödinger• Used de Broglie wavelength to

create a quantum theory based on waves

• Did not keep the "orbits"

• The wave/particle model cannot determine the location and momentum of an electron at the same time

• The quantum model predicts the probability that an e- is at a specific location

Heisenberg Uncertainty Principle• Can only determine the

location or the momentum (velocity) of the particle - not both at the same time!

Photons and Photoelectric Effect

Photoelectric Effect

• Metal is illuminated by electromagnetic radiation

• Energy that is absorbed near the surface can free electrons, causing e's to fly off

• Released electrons are called photoelectrons

• Significant time delay between the illumination and ejection - build up of KE to free e-'s

• Increasing the intensity of light = cause electrons to leave with greater KE

• Photoelectrons would be released regardless of frequency of light, as long as the intensity was great enough....

But these are FALSE!

Wave theory predicts the following:

Photoelectric Effect Findings

• Photons were ejected immediately

• Increasing the intensity did not change the KE although more e-'s were ejected, KE does not increase.

• If the frequency fell below a threshold (specific for each metal), no photoelectrons would be ejected, regardless of intensity!

• If the frequency increases above the threshold, KE increases linearly

PE Effect - Math

• Threshold Frequency

• Work Function - the minimum amount of energy required on a metal surface to eject an electron

• How are these two related?

PE Effect - Math

Photoelectric Effect