Electromagnetic Radiation and Quantum Phenomena

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Define photon
A discrete wave-packet of electromagnetic waves
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Define excitation
The movement of an electron to a higher energy level in an atom
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Defie de-excitation
The movement of an electron to a lower energy level or ground state in an atom
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Define ionisation
The process where an electron is removed from (the ground state) or added to an atom
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Define electron-Volt
The kinetic energy carried by an electron after it has been accelerated from rest through a potential difference of 1 volt
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Define work function
The minimum amount of energy needed to break the bonds between the metal and the electron so the electron can escape from the surface. The value depends on the metal
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Define threshold frequency
The lowest frequency of light that when shone on a metal will cause electrons to be released from it by the photoelectric effect
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Define stopping potential
The potential difference needed to stop the fastest moving electrons with maximum kinetic energy
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Define photoelectric effect
The emission of electrons from a metal when a light of a high enough frequency is shone on it
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Step 1 of photoelectric effect
Free e- on the surface of the metal absorb energy from the light
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Step 2 of photoelectric effect
If the e- absorbs enough energy the bonds holding it to the metal break and the e- is released
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Step 3 of photoelectric effect
The e- emitted are called photoelectrons
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Experiment Conclusion 1 (not explained by wave theory)
For a given metal, no photoelectrons are emitted below a certain frequency
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Experiment conclusion 2 (not explained by wave theory)
The photoelectrons are emitted with a variety of kinetic energies from zero to maximum value. This value of maximum kinetic energy increases with the frequency of the radiation and is unaffected by its intensity
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Experiment conclusion 3
The number of photoelectrons emitted per second is proportional to the intensity of the radiation
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What is the wave-particle duality theory?
If 'wave-like' light showed particle properties (photons), 'particles' like electrons should be expected to show wave-like properties
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What does the wave theory suggest?
For a particular frequency of light, the energy is proportional to intensity; the energy carried would be spread evenly over the wavefront; each free e- would gain a bit of energy from the incoming wave and gradually each e- would gain enough energy
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Why doesn't wave theory explain the photoelectric effect?
The kinetic energy doesn't increase with intensity, the electrons are never emitted at certain frequencies, there is no explanation for the threshold frequency or for the maximum kinetic energy of the e- depending only on the frequency
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Why do the electrons have a range of kinetic energies?
Electrons deeper down in the metal will lose more energy as they require more energy to remove them
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What is the maximum kinetic energy?
hf minus the work function
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Why can the photon emitted during de-excitation be only of a certain allowed energy?
The transitions are between definite energy levels
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What does Einstein's photon model of light say?
EM waves and their energy exist in discrete packets called photons, the energy carried by one photon is E=hf
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What did Einstein see?
The photons have a one-on-one particle-like interaction with an e- on the metal's surface, and a photon would transfer all its energy to one electron
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What happens according to the photon model?
When light hits the surface, the metal is bombarded by photons. If one of these photons collides with a free electron, the electron will gain energy equal to hf
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Card 2


Define excitation



Card 3


Defie de-excitation


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Card 4


Define ionisation


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Card 5


Define electron-Volt


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