past paper notes- Quantum physics Flashcards
State an effect, one in each case that provides evidence for:
(i) the wave nature of a particle: electron diffraction
(ii) the particulate nature of electromagnetic radiation: photoelectric effect
Explain why, for any particular wavelength of electromagnetic radiation, most of the electrons are emitted with kinetic energies less than the maximum value EMAX.
maximum KE when electron is emitted from the surface
energy is required to bring electron to surface
Explain why kinetic energy of an electron is independent of the intensity of the incident radiation? /3
frequency determines the energy of photon
intensity determines the number of photons. intensity does not determine the energy of photon
kinetic energy of the electron depends on the energy of one photon
Work function should be greater than energy of photon for photoelectric emission
State three pieces of evidence provided by the photoelectric effect for particulate nature of electromagnetic radiation? /3
1) energy of photon is depended on frequency
2) energy of emitted photon is not depend on intensity
3) rate of emission of electrons depends on intensity at constant frequency
absorption spectrum- arrow is upwards
emission spectrum- arrow is downwards
gradiant of Emax and 1/lambda is hc
Describe the appearance of a visible line emission spectrum, as seen using diffraction grating? /2
1) mostly dark background
2) coloured lines
The spectrum of the light emerging from the cloud of cool gas is viewed using a diffraction grating.
Explain why this spectrum contains a number of dark lines. /3
electrons in gas interact with photons
photon causes electron to move to higher energy level
photon energy= difference in energy of electron energy levels
when electrons de-excite, photons emitted in all directions so there is a dark line
Suggest an explanation for why people are not observed to diffract when they walk through a
doorway. /1
wavelength negligible compared with width of doorway
A beam of white light passes through a cloud of cool gas. The spectrum of the transmitted
light is viewed and contains a number of dark lines.
Explain why these dark lines occur. /4
photons absorbed by electron and electron excited
photon energy is equal to difference in energy of two energy levels
photon energy relates to single wavelength
electron de-excites and emits photon in any direction
increasing intensity does not increase Emax instead rate of ejection increases
increasing frequency, decreases the rate of ejection and increases Emax
