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THE PHOTOELECTRIC EFFECT
· Shining light on a metal will emit electrons
· If the surface electrons receive enough energy the
bonds holding them will break and the electron will
be released
· No electrons are emitted if the radiation is below a
certain frequency, known as the THRESHOLD
FREQUENCY
· The electrons are emitted with a range of kinetic
energies, these increase with the frequency but are
unaffected by the intensity
· The number of electrons emitted is proportional to
the intensity…read more

Slide 3

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THE PHOTOELECTRIC EFFECT
· Can't be explained by wave theory
· Can be explained by particle theory
· The minimum energy needed to free an electron
from the metal is called the WORK FUNCTION
ENERGY ()
· Energy gained by the electron is given by hf, f=/h
· The kinetic energy of the electron is hf minus any
energy it has lost, namely the work function energy
· hf=+1/2mv2
· The kinetic energy is not affected by intensity
because electrons only absorb one photon at a
time.…read more

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ENERGY LEVELS AND PHOTON EMISSION
· Electrons in atoms can only exist at defined
energy levels
· They can move down energy levels by
emitting a photon
· Since the energy levels are specific values, the
energy of an emitted photon can only be
certain value
· The energy carried by each photon is equal to
the difference in energies between two levels.
· E=E2-E1=hf=hc/…read more

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ENERGY LEVELS AND PHOTON EMISSION
· EMISSION SPECTRA: Produced by hot gases
· When a gas is heated the electrons move to higher
energy levels
· When they fall back to the GROUND STATE
(minimum energy level) they emit the energy
change as photons
· This produces a line spectrum when diffracted
· Each line corresponds to a particular wavelength of
light, and since only certain photon energies can
happen, you only see the corresponding
wavelength.…read more

Slide 6

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ENERGY LEVELS AND PHOTON EMISSION
· ABSORBTION SPECTRA: Hot things produce
continuous spectra
· If this light passes through a cool gas, the electrons
move to higher energy levels by absorbing photons
with the right wavelength/energy to move them to
a higher energy level
· These wavelengths are then missing from the
spectrum leaving black lines
· As before, they correspond to the specific energy
changes and wavelengths of light…read more

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