Flashcards in Electromagnetic Radiation and Quantum Phenomena Deck (68)
What happens if you shine radiation of high enough frequency onto the surface of a metal?
It will emit electrons
For most metals, what range is the frequency of radiation necessary for the metal to emit electrons?
In the UV range
What is the photoelectric effect?
The emission of electrons from a metal when light of high enough frequency is shone on it
What are the electrons that are emitted from a metal called?
Why does shining radiation of high enough frequency onto a metal surface make electrons be released?
Metals contain free electrons on the inside, which absorbs energy from the radiation, making it vibrate. If an electron absorbs enough energy, the bonds holding it to the metal will break and the electron is released
What is the minimum frequency of radiation needed for a given metal to emit electrons called?
The photoelectrons are emitted with a variety of.... This value of maximum.... increases with....?
The photoelectrons are emitted with a variety of kinetic energies. This value of maximum kinetic energy increases with the frequency of the radiation
What is the intensity of radiation on a metal?
The amount of energy per second hitting an area of the metal
For the photoelectric effect, what is unaffected by varying the intensity of radiation?
The maximum kinetic energies of the photoelectrons
What is proportional to the intensity of the radiation for the photoelectric effect?
The number of photoelectrons emitted per second
Why can't wave theory explain the photoelectric effect?
The energy of a wave is proportional to its intensity. Increasing the intensity of the waves should increase the energy of the electrons that are emitted from the metal, but this doesn't happen
What does the photoelectric effect show about light?
That light can't just act as a wave
What are the discrete packets of EM waves also known as?
Who discovered the discrete packets of EM waves?
What did Einstein suggest about EM waves?
He suggested that waves can only exist in discrete packets that he called photons
What is the photon model, developed by Einstein, which can explain the photoelectric effect?
He saw these photons of light as having a particle-like interaction with an electron in the metal surface, where each photon transferred all its energy to one specific electron
Why can't visible light be used to demonstrate the photoelectric effect?
It's not got a high enough frequency
What is the work function?
The minimum amount of energy needed for an electron to escape a metals surface
What does the energy have to be compared to the work function for an electron to be emitted?
Energy has to be greater than the work function
What happens if the energy of a photon is less than the work function of the metal?
The electron will shake a bit then release it's energy as a photon
What is the equation for the threshold frequency?
Threshold frequency = Work function / Planck's constant
How do solar cells use the photoelectric effect?
They convert light energy into electricity
What is the energy transferred from EM radiation to an electron equal to?
The energy the electron absorbs from one photon, hf
What is the kinetic energy as the electron leaves the metal equal to?
hf (energy of photon) minus any other energy losses
Why do electrons emitted from metals have a range of different kinetic energies?
Because they all have different energy losses
What is the minimum amount of energy an electron can lose equal to?
The work function
What is the photoelectric equation?
hf = work function + max kinetic energy
hf = Φ + E k max
hf = Φ + 0.5 m (Vmax)^2
What is the intensity of photons?
The number of photons per second on an area
What effect on the kinetic energy of the electrons does increasing the intensity of photons?
Doesn't have an effect