2- quantum phenomena

the photoelectric effect

the photoelectric effect

light above a certain frequency is incident ona metal surface cuaisng electrons to be emitted from the surface

key points about the photoelectric effect (5)

1. photoelectrons are only emitted is the frequecny is above the threshold frequency

2. the maximum kinetuc energy of the electrons does not increase when light intensity is increased

3. light intensity increasing increases the number of photoelectrons emitted

4. increased frequency increases the kinetic energy of the photolectrons

5. there is a one to one interaction between photons and electrons

Photon energy equation

E= hf

where

E= photon energy

h= plancks constant

f= photon energy

threshold frequency equation

where-

the f is the threshold frequency in hz required for electrons to be emitted

the o is the work function in joules (minimum photon energy)

h is planck’s constant

maximum photoelectron kinetic energy derivation

Emax = h f - Φ

where h is plancks constant , f is frequency and Φ is the work function

OR

½ mv2max = hf -Φ

where m is mass v is velocity h is planck’s constant and f is frequency, and Φ is the work function

stopping potential definition and equation

when photoelctrons are stopped by going against a potential difference v the potential which stops the elctrons is known as the stoppping potential

the equation for this is eVs = Ekmax

where e is electron charge, vs is stopping potential and Ekmax is the maximum potential energy

atomic energy levels

elctrons orbit certain energy levels given the number n. n =1 is the ground stater and subsequent n values are excited energy states. electrons can jump between and occupy these energy states through abosrption where they go up and emission where they go down.

phton energy through emission/ absorption equation

ΔE= Ef - Ei where delta E is photon energy Ef is final energy and Ei is initial energy

evidence for light exhibiting wave particle duality

wave properties= interference and diffraction patterns

particle properties= the photoelectric effect

de broglie wavelength equations and definition

the realtion of wavelength to the momentum of a particle through

λ = h/p

and this can be rearranged to

λ= h/ mv

where

λ is wavelength in metres

h is planck’s constant and p is momentum in kg m s-1

key observations of electron diffraction experiments

electron diffraction patterns have similar spacing to x ray diffraction patterns, faster electrons diffract less

showing that: faster electrons have shorter wavelengths and vice versa

line emission/ absorption spectra

when excited gases are passed through a prism wavelngths are seperated in to a spectrum, with each line corresponding to a wavelngth. each element has a unique line emission spectra.

when white light passes through a gas a line absorption spectra is released, which will match with the emission spectra.