chapter 13 - Quantum physics Flashcards
what are photons
discrete energy quanta (packets)
Energy equations
E = hf = hc/λ
define one electron volt eV
the energy transferred when one electron travels through a potential difference of one volt
Energy of a photon
W = QV so 1.6x10^-19 x 1
Define the photo electric effect
when electromagnetic radiation is incident on a metal, photoelectrons are released from the surface of the metal
work function ϕ
minimum amount of energy required to free an electron from the surface of the metal, as E=hf therefore there is a threshold frequency that the incident light needs to have to excite the electrons enough to give them enough energy to escape
Einsteins photo electric equation
hf = ϕ + KEmax
why do we use KE max in the photoelectric equation
some electrons require more energy to be released if they are closer to their respective nucleus’, therefore more than the work function is needed therefore less energy is left over for KE
what does photoelectric emission depend on?
Frequency, not intensity of light. If the incident frequency is less than the threshold frequency, no photo electrons are emitted, regardless of intensity. However if the incident frequency is above the threshold frequency, increasing the intensity increases the emission rate. This is because intensity is the amount of electrons emitted per second so as the reactions are one to one, increasing intensity increases the amount of electrons available to react and therefore the emission rate.
how do you increase the KE of the emitted photo electrons?
increase the frequency of incident light so left over energy converted to KE is higher.
de broglie equation
λ = h/momentum = h/mv
