Elecromagnetic Radiation And Quantum Flashcards
What is the photoelectric effect?
It is where photoelectrons are emitted from the surface of a metal after light above a certain frequency is shone upon it.
What is the Threshold frequency?
It is the minimum frequency of light needed to cause electrons to be emitted.
When an experiment on the photoelectric effect is done with a zinc plate, What conclusions can be made from the results of the experiment?
- For a given metal, no photoelectrons are emitted if the radiation has a frequency below the threshold frequency.
- The photoelectrons are emitted with a variety of kinetic energies ranging form zero to some maximum value (this depends on the frequency of the radiation).
- The intensity of the radiation is the amount of energy per second hitting an area on the metal.
- The number of photoelectrons emitted per second is proportional to the intensity of the radiation.
Could the threshold frequency be explained through wave theory? Why?
No. as it suggests that any frequency of light should be able to cause photoelectric emission as the energy absorbed by each electron will gradually increase with each incoming wave.
Could the threshold frequency be explained through the photon model of light? Why?
Yes. This is because the photon model of light suggests that:
- EM waves travel in discrete packets called photons, which have an energy which is directly proportional to its frequency.
- Each electron can absorb a single photon, therefore a photoelectron is only emitted when frequency of wave is above the threshold frequency.
- If the intensity of the light is increased, and frequency of the wave is above the threshold frequency, more photoelectrons will be emitted.
What conclusions does the photon model of light produce?
- EM waves travel in discrete packets called photons, which have an energy which is directly proportional to its frequency.
- Each electron can absorb a single photon, therefore a photoelectron is only emitted when frequency of wave is above the threshold frequency.
- If the intensity of the light is increased, and frequency of the wave is above the threshold frequency, more photoelectrons will be emitted.
What is the work function?
The minimum amount of energy which is required to remove an electron from the surface of a given solid.
What is stopping potential?
The potential difference you would need to apply across the metal to stop the photoelectrons with the maximum kinetic energy.
What is a fluorescent tube?
It is a tube filled with mercury vapour, across which a high voltage is applied.
How is a fluorescent tube used?
A high voltage is run across the fluorescent tube, which accelerates free electrons through the tube, which then collide with the mercury atoms causing them to become ionised, releasing more electrons. When they de-excite, they release photons (most of which within the UV range). The phosphorous fluorescent coating on the inside if the tube absorbs these UV photons and therefore, electrons in the atoms of the coating become excited and then de-excited, releasing photons of visible light.
What is line emission spectra?
A spectrum of the wavelengths of light emitted from an element when it’s electrons lose energy.
Electrons must pass through an ionised gas.
What is a continuous spectra?
A spectrum of white light that allows all wavelengths as electrons are not confined to energy levels in the object producing the spectrum.
What is line absorption spectra?
When a continuous spectra is shone through a cool gas, photons of the correct wavelength will be absorbed by the electrons to excite then to higher energy levels.
What is an electron volt?
The energy gained by an electron when it is passing through a potential difference of one volt.
Light and electrons both have wave and particle properties.
Give one example of light having each of these properties.
Particle: Photoelectric effect
Wave: Diffraction and interference
