3.2.2: Ectromagnetic Radiation And Quantum Phenomena Flashcards
(23 cards)
What is the photoelectric effect?
When photoelectrons are emitted from the surface of a metal after light above a certain frequency is shone on it.
What is the threshold frequency?
The minimum frequency of light required to produce the photoelectric effect.
What is the photon model of light?
- EM waves travel in discrete packets called photons, which have an energy that is directly proportional to frequency.
- Each electron can absorb a single photon; therefore, a photoelectron is only emitted if the frequency is above the threshold frequency.
- If the intensity of the light is increased, if the frequency is above the threshold, more photoelectrons are emitted per second.
What is the work function?
The minimum energy required for electrons to be emitted from the surface of a metal.
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 the photoelectric equation?
hf = φ + KE_max.
How to find the max kinetic energy of the released photoelectrons?
Ek(max) = eVs.
Vs is the stopping potential and e is the charge of an electron.
What is excitation?
When electrons move up an energy level by gaining energy from a collision, they are said to be in an excited state.
What is ionisation?
When an atom gains or loses an electron to become charged.
When does ionisation occur?
If the energy of the free electron is greater than the ionisation energy.
What happens if an electron becomes excited?
It will quickly return to its original energy level and release the energy it gained as a photon.
How does ionisation and excitation work in the fluorescent tube?
- Voltage accelerates free electrons.
- They collide with mercury, making them ionised, releasing free electrons.
- Electrons collide with mercury atoms, making them excited.
- Release photons when decited.
- Fluorescent coating absorbs UV photons.
- Electrons release photons of visible light.
What is an electron volt?
The energy gained by an electron passing through a potential difference of 1V.
What is the formula for energy?
Energy = charge x voltage.
How do you get a line spectrum?
By passing the light from a fluorescent tube through a diffraction grating or prism.
What does each line represent in a line spectrum?
A different wavelength of light emitted by the tube.
How do we know electrons can only transition between discrete energy levels?
As the spectrum only contains discrete values of wavelengths, the only photon energies emitted will correspond to these wavelengths.
How do you get a line absorption spectrum?
By passing white light through a cooled gas.
What do the lines on a line absorption spectrum represent?
Possible differences in energy levels as the atoms in the gas can only absorb photons of an energy equal to the exact difference between two energy levels.
What does the equation hf = e1 - e2 represent?
The energy difference between 2 atomic energy levels.
What does electron diffraction suggest?
Particles possess wave properties.
What does the photoelectric effect suggest?
That electromagnetic waves have a particulate nature.
What is the de Broglie equation?
λ = h/mv, predicts that all moving particles have wave characteristics.
