4.5 Quantum Physics Flashcards
how does electromagnetic radiation travel through space
as a continuous wave
what happens when electromagnetic radiation interacts with matter
it interacts as discrete energy quanta (packets) called photons
what is the relationship between energy of a photon and the frequency of electromagnetic radation
energy of a photon is directly proportional to the frequency of the electromagnetic radiation
whats the equation for energy of electromagnetic radiation
E=hf or E=hc/λ where
E=energy of a photon [eV]
f=frequency of EM radiation [Hz]
h= Planck constant
c= speed of light [ms^-1]
λ=wavelength [m]
what is the value of the Planck constant
6.63x10^-34
what is an electronvolt defined as
the energy transferred when an electron travels through a potential difference of 1 volt
how can an electronvolt be substituted into a joule
using W=VQ
-> eV x e-= J so 1eV= 1.6x10^-19J
what is the photoelectric effect
when electromagnetic radiation is shone on to a metal, electron are released from the surface of the metal
what is the photoelectric equation
hf=ϕ + KE max
h= Plancks constant
f= frequency of electromagnetic radiation
ϕ= the work function of the metal
KE max= the maximum kinetic energy of the released electron
why is the maximum kinetic energy used in the photoelectric effect
because some electrons may be closer to the nucleus, requiring more energy than the work function amount to be released, leaving less energy left over as kinetic energy
what is the threshold frequency
the minimum frequency of incident radiation for electrons to be released
how does increasing the intensity of the incident radiation effect the rate of electron emission
the rate of electron emission is increased
why does the rate of electron emission increase when the intensity of radiation is increased
the increase in intensity increases the number of photons available to interact with the electrons
how can the kinetic energy of electrons released be increased
increase the frequency of radiation further above the threshold frequency, so there is more energy left over to be converted to kinetic energy
how can LEDs be used to determine the Planck constant experimentally
-LEDs only emit light when the pd across them exceeds the threshold pd required
-potential divider set up to vary the voltage
-place small black tube to make it more obvious when the LED has lit up
-vary the pd to determine the threshold pd
-as the LED produces light of a specific colour we know the wavelength of the light
-use eV=hc/λ to determine the Planck constant
how can the accuracy of the LED experiment to determine the Planck constant be increased
-use a variety of different coloured LEDs which each emit different wavelengths of light
-values of wavelengths and threshold pd for each can be recorded and a graph of V against 1/λ can be drawn
-the gradient is equal to hc/e -> as the speed of light and electron charge are known constants, h can be calculated
