3- quantum phenomena Flashcards
what are properties of particles
-have mass
-have kinetic energy
- have momentum
-obey newtons laws of motion
travel in straight lines unless a force acts on them
keep their energy until they interact
wave properties
-no mass
-no kinetic energy
-no momentum
-do not obey newtons laws of motion
-reflect
-refract
-diffract
-lose energy as they leave the source
what is the photoelectric effect
when electromagnetic radiation is incident on a metal surface causing the EM radiation to be absorbed by electrons causing them to be emitted from the surface of the metal
how can the photoelectric effect be demonstrated
electroscope
what are electrons removed by the photoelectric effect called
photoelectrons
how do we know light is quantisised/ carried in discrete packets
because each electron can only absorb one photon
how does the electroscope work
-the electroscope is given a negative charge there4 the gold leaf is also negatively charged
-the gold leaf moves away from the anode due to repulsion
-when EM radiation is incident on the metal plate, the gold leaf will slowly fall
-this is due to the metal plate losing electrons due to the photoelectric effect there4 the electrons from the gold leaf will travel up the anode to replace the electrons lost by thermal metal plate
what is the threshold frequency
the minimum frequency of incident EM radiation required for photoemission to take place
what is the threshold wavelength
the longest wavelength of incident EM radiation that would remove an electron from the surface of a metal
equation relating frequency and wavelength
v= f λ
v= wave speed
f= frequency
λ= wavelength
what does the intensity of the radiation effect
the number of electron emitted per second by photoelectric emission
what happens when you increase the frequency of the radiation
you increase the kinetic energy of the photoelectron
what is the equation linking the amount of energy of each photon to the frequency of EM radiation
E= hf
E= energy of photon
or
E= hc/ λ
c= speed of light
what is the work function (Φ ) threshold of a material
the minimum energy required to release a photoelectron from the surface of a metal
photoemmison for UV light, Blue light and red light
UV- a lot of energy so electron leaves surface w extra energy converted to kinetic energy as it moves away
blue- lower energy than UV, electron leaves metal surface but not enough energy left over as KE
red- low energy, photoemission does not occur
why do alkali metals have lower threshold frequency’s like visible light
because the attractive forces between the electrons and and the positive metal ions are relatively weak
why do transition metals have higher threshold frequency’s
because attractive forces between electrons and and positive metal ions are much stronger
what is the photoelectric equation
hf= Φ + Ek
Ek= kinetic energy
hf= energy of photon
threshold frequency equation
Fo = Φ/ h
what is stopping potential (Vs)
the potential difference required to stop photoelectric emission from occurring
how do you each stopping potential
by increasing the emf of the supply until a p.d is reached at which no electrons can cross a gap
what is the stopping potential (Vs) equations
Vs= w/Q =. E/Q. = Ek max/ e
e= charge of an electron
what happens to photoelectric current when frequency is increased but intensity is kept constant
photoelectric current will decrease
how do you convert joules to electron volts J- eV
1eV= 1.6x10^-19 J
eV to J = x1.6x10^-19
J to eV = / 1.6x10^-19
what is intensity
the rate of energy transferred per unit area
why is there a maximum kinetic energy
because some electrons are neared to the surface of the metal than others meaning less energy is used to remove them from the surface resulting in those photoelectrons having more Ke than those deeper in the metal
what is photoelectric current
a measure of the number of photoelectrons emitted per second
how do you calculate photoelectric current
number of electrons emitted. x charge on one electron
what is the calculation for intensity
intensity = nhf/ tA
n= number of photons
t= time
A= area
how do electrons move from one energy level to another to another
by absorbing or emitting emitting a photon
what is the ground state
the lowest energy level, where the electron is usually found as it is the most stable configuration of the atom
what happens to energy levels when a photon is emitted by an electron
the electron moves from a higher energy level to a lower energy level
what is excitation
when an electron absorbs a photon of energy and moves from the ground state to a higher energy level
what is the difference between two energy levels equal to
a specific photon energy
what equation relates wave length and energy difference
λ= hc/ E2- E1
what is ionization
when an atom gains or loses an orbital electron and becomes charged
what is ionization energy of an atom
the minimum energy required to remove an electron from the ground state of an atom
what does it mean when an element fluoresces
it means the element absorbs photons of UV light and them emits photons of visible light
what are fluorescent tubes
partially evacuated glass tubes filled with low pressure mercury vapour with a phosphor coating on the glass
how does a line spectra occur
when excited atoms emit light of certain wavelengths which correspond to different colours
what are the two types of line spectra
emission spectra
absorption spectra
what can the wave theory of light be used to explain
effects such as reflection, refraction, diffraction, polarization and interference
what is young’s double split experiment
a light is passed through a slit with a width of similar side to their de brogile wavelength, this causes the wave to spread out forming a diffraction pattern
why is graphite film ideal for electron diffraction
because of its crystalline structure. the gaps between atoms in the crystals act as slits, allowing the electron waves to spread out and create a diffraction pattern
how do you increase the diameter of the ring diffraction pattern
by lowering the accelerating voltage
how do you decrease the diameter of the ring diffraction pattern
by increasing the accelerating voltage
what happens to the electron wavelength when you decrease the momentum
the wavelength will increase
what happens to electron wavelength when you increase the speed
the wavelength will shorten
what is the equation of de broglie wavelength in terms of the kinetic energy of the particle
λ = h / √ 2mE
