M4.3 Quantum Physics Flashcards
why are electron energy levels negative
because its the amount of energy the electron needs to gain to escape.
how do electromagnetic waves act when interacting with matter
as discrete packets
Photons
define Photon
Discrete packets of EM radiation
massless
Define an electron Volt and where does it come from
Unit of energy
energy
Kinetic energy gained from electric potential when accelerated through 1 p.d
Describe a experiment to calculate plancks constant
LED
use a potentiometer to change the voltage applied
increase voltage until at threshold voltage
note down threshold voltage and wavelength of the light emitted from the LED
energy of the electrons = energy of the light emitted
ev = hf
v = (h/e)f
calculate f with wavelength and speed of light
straight line graph
gradient = h/e
describe the photoelectric effect
the mission of electrons when EM radiation hits a material
Describe an experiment to view the photoelectric effect
create a circuit with a gap
one end of the gap there is a anode and the other theres a cathode
both electrodes are metal
shine different coloured light at the anode
blue should generate a current and red won’t
Incident waves must be above a threshold energy to generate a current
greater intensity – blue - more electrons are knocked out but they dont move quicker - Red -nothing happens
what did einstein conclude from the photoelectric efffect
light can behave a particle
each electron needs a specific amount of energy to escape the metal
if the energy of a photon was below the energy required to escape as there is a one to one relationship between photons and electrons
hence no time delay
define the work function of a material
Property of th material
energy required to allow a surface electron to escape with 0 kinetic enegry
how can you use a gold leaf electroscope to prove the photoelectric effect
Negatively charge the electroscope initially so the leaves are repelling each other
then shine UV light on the zinc plate at the top then it will emit electrons gradually getting less negatively charged eventually stop repelling each other.
explain a practical that can be done to show that an electron can act as a wave
use an electron diffraction tube
where electrons are accelerated through a high voltage
through a thin graphite film electrons cause a diffraction pattern on the phosphorus screen
why is graphite used when creating a interference pattern of electrons
because the gaps electrons pass through are similar a size to the de broglie wavelength
and crystaline carbon structure makes it ideal
Roughly what is the de brogile wavelength of an electron passing through some crystaline substance
Was a Multiple choic question so important and could be useful to know your roughly right on a calculation question
10^-10
