The Photo Electric Effect. Discovery, implications, and current technology. Presentation by Ryan Smith. Discovery: Heinrich Hertz and Phillip Lenard. Hertz clarified Maxwell ’ s electromagnetic theory of light: Proved that electricity can be transmitted in electromagnetic waves.
Discovery, implications, and current technology
Presentation by Ryan Smith
Back in 1887…
His assistant, Phillip Lenard, explored the effect further. He built his own apparatus called a “phototube” to determine the nature of the effect:
By varying the voltage on a negatively charged grid between the ejecting surface and the collector plate, Lenard was able to:
KEmax = eVstopping
Classical physics failed to explain this,
Lenard won the Nobel Prize in Physics in 1905.
A new theory of light:
This was published in his famous 1905 paper:
“On a Heuristic Point of View About the Creation and Conversion of Light”
Einstein predicted that a graph of the maximum kinetic energy versus frequency would be a straight line, given by the linear relation:
KE = hv - Φ
…Therefore light energy comes in multiples of hv
“…There are therefore now two theories of light, both indispensable, and - as one must admit today despite twenty years of tremendous effort on the part of theoretical physicists - without any logical connection.”
*This work won Einstein his Nobel Prize in 1922.*
Electrons must exist only at specific energy levels within an atom
ΦWork Function ≈ Ionization Energy
Another Discovery is under way….
The PhotoVoltaic Effect:
*extra positive “holes”
from electron vacancies
*extra negative electrons
An equilibrium is reached where a net charge concentration exists on each side of the junction.
Austin, Geoff. Jan 2005. Photo Electric Effect. Retrieved 10-23-05.
Einstein, Albert. (1905). “On a Heuristic Viewpoint Concerning the Production and Transformation of Light.” Annalen der Physik, Vol 17, 132.
Elert, Glenn. Photoelectric Effect. Retrieved 10-28-05.
Hamakawa, Yoshihiro. (2004). Thin-Film Solar Cells: Next generation photovoltaics and its application. New York: Springer.
Lenardic, Denis. A Walk Through Time. Retrieved 11-12-05. http://www.pvresources.com/en/history.php
U.S. DOE Photovoltaics Program. (2005). Photovoltaics Timeline. Retrieved 10-27-05. http://inventors.about.com/library/inventors/blsolar2.html
n.a. n.d. Philipp Lenard – Biography. Retrieved 10-23-05.
n.a. n.d. The Photo Electric Effect. Retrieved 10-06-05.
n.a. n.d. The Electric Field In Action. Retrieved 11-12-05. http://www.sandia.gov/pv/docs/PVFEffElectric_Field.htm
n.a. n.d. Timeline of Solar Cells. Retrieved 10-27-05. http://www.nationmaster.com/encyclopedia/Timeline-of-solar-cells
Robertson, E F. O’Conner, J J. A history of Quantum Mechanics. Retrieved 10-25-05.
Smith, Willoughby. (1873). "Effect of Light on Selenium during the passage of an Electric Current".Nature, Vol ? 303.
Available URL: http://histv2.free.fr/selenium/smith.htm