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.
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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
Another Discovery is under way….
*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.
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