Studied by 12 people
How does electromagnetic radiation travel through space?
As a continuous wave
What are photons?
Discrete energy packets
When does electromagnetic radiation act as photons?
When it interacts with matters
What is the equation linking energy of a photon to frequency of the electromagnetic radiation?
E = hf = hc / lamda
What is h?
Planck constant
6.63×10^-34
What is 1 electronvolt?
The energy transferred when an electron travels through a potential difference of 1 volt
What is 1 electronvolt in joules?
1eV = 1.60×10^-19J
What is the photoelectric effect?
When electromagnetic radiation is shone onto a metal electrons are released from the surface
What happens if you try to use visible light for the photoelectric effect?
No electrons will be removed from the plate
What is the work function of a metal?
Minimum energy required to free an electron from the surface of the metal
What must a photon have in order to free an electron from a metal surface?
Energy at least as great as the work function
What is threshold frequency?
Minimum frequency required of the electromagnetic radiation to free electrons from the surface of the metal
Does visible light produce the photoelectric effect?
No as the frequency is too low
What is the photoelectric equation?
hf = phi + KEmax
phi = work function of the metal
KEmax = max ke of released electron
What determines the KE of a released electron?
Amount of energy left after it is released (after using up work function amount)
How does intensity of radiation relate to electron emission if frequency < threshold frequency?
no electrons will be released regardless
How does intensity of radiation relate to electron emission if frequency > threshold frequency?
increasing intensity increases rate of electron emission as it increases the number of photons available to interact with the electrons
How can you increase the kinetic energy of the released electrons?
Increase the frequency of radiation further above the threshold so there's more energy left over
What is wave particle duality?
diffraction and superposition of light relies on the radiation acting as a wave
Photoelectric effect relies on it acting as discrete photons
Therefore electromagnetic waves have a dual nature
What is the de broglie equation?
Lamda = h/p = h/mv
What can the de Broglie equation be applied to?
All particles with mass
How can electrons be used as evidence for wave-particle duality?
electrons are particles with mass and charge, they can be accelerated and deflected by magnetic and electric fields
However they can also be made to diffract when fired at thin polycrystalline graphite which is a property of waves
Note
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