Photons & Spectra Flashcards
What is a photon?
A “packet” of electromagnetic energy - the smallest amount of energy a particular frequency carries
What is the equation for photon energy?
E = hf
How is the energy of a photon related to its frequency?
Energy is directly proportional to frequency
What is the value of Planck’s constant, h?
h = 6.63 x 10-34 Js
What does “quantisation” of energy in an atom mean?
Electrons can only have discrete, fixed energies within an atom. These energy levels are different for different elements and depend on the state of the element (ie solid, liquid or gas).
How can a photon interact with an electron in an atom?
If the photon energy (consequently it’s frequency) exactly matches the difference in energy levels, the electron will absorb the photon.
If it does not match the difference in energy levels, it will not be absorbed.
If it is greater than the work function, it will be absorbed and the a photoelectron will be emitted.
How can an electron interact with an electron in an atom?
Some of the incident electron’s kinetic energy will be absorbed and the atomic electron will move to an excited state.
How does a flourescent lamp work?
Low pressure gas is ionised by a potential difference.
A current (electrons) flows.
These electrons excite the gas molecules.
Electrons in the gas molecules move up energy levels.
When they drop energy levels they emit characteristic photons in the UV range.
These photons are absorbed by the flourescent coating and then re-emitted in the visible range.
What is the photoelectric effect?
Incident photons on a metal carry enough energy to overcome the work function. Photoelectrons are emitted provided the frequency of the incident photons are greater than the threshold frequency.
