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Page 1

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Introduction
Forget about electron
energy levels for this topic.

The Photoelectric Effect
only works on electrons
which have already been
knocked out of their
atomic orbits but are still
inside the material (i.e.
free or "delocalised"
electrons).

Page 2

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Photoelectric
Effect

VIDEO

...of a simulation of the
Photoelectric Effect.

Page 3

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Overview
Electromagnetic radiation
(EMR) of sufficiently high
energy can cause
delocalised (i.e. free)
electrons to leave the
surface of a suitable
material.

Page 4

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Importance
The Photoelectric Effect is
an important piece of
evidence which proves the
Photon Model of Light.
The Wave Model of Light
cannot explain the effect.

Page 5

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Photoelectric
Effect
Electrons which gain
sufficient K.E. from EMR
photons to escape the
material are called
Photoelectrons. (i.e.
Photoelectrons are just
ordinary electrons which
have gained their kinetic
energy from a photon)

Page 6

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Photoelectric
Equation
hf = + Ek(max)
hf is the energy the
incoming photon (which
gets absorbed by one
electron)
is the Work Function.
Ek(max) is the maximum
Kinetic Energy of the
ejected Photoelectron.

Page 7

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Photoelectric
Equation

hf = + Ek(max)
is the Work Function. It
is the minimum energy (J)
needed to remove an
electron from the surface
of a material

Page 8

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Photoelectric
Equation

hf = + Ek(max)
If hf < then no electron
will be able to leave the
material surface, no
matter how intense the
photon source

Page 9

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Photoelectric
Equation

hf = + Ek(max)
If hfo = then
photoemission is about to
begin. The frequency of
the photon is called the
Threshold Frequency (fo).
Again, intensity changes
have no effect.

Page 10

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Photoelectric
Equation

hf = + Ek(max)
If hf > then
photoelectrons will be
emitted with a range of
kinetic energies up to a
maximum value given by
Ek(max)

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