2.7 photons Flashcards
what are photons
discrete packets of energy
what quantity can be measure in eV
energy
what is the photoelectric effect
the emission of an electron from a surface due to light or em radiation
Which features of the photoelectric effect can’t be explained if light is a wave?
if light was a wave, the energy of the electrons released would increase with increasing intensity of the light - but instead the energy of the electrons depends on frequency (and no electrons are released below a certain threshold value, no matter how intense the light is).
work function
the minimum energy required for an electron to be released from a materials surface
True or false? The rate of emission of photoelectrons is proportional to intensity (provided the light is above the threshold frequency).
True.
Higher intensity means more photons, this means a higher rate at which electrons can absorb energy and be released
What experimental evidence appears to show particles behaving as waves?
Electron diffraction.
Electrons will diffract when passed through the spaces between atoms in graphite (like a tiny diffraction grating).
This wouldn’t happen if electrons were behaving as particles only.
What is a line spectra
a series of discrete wavelengths of light emitted or absorbed by atoms when electrons transition between energy levels
What causes an emission line spectra
when electrons fall from higher to lower energy levels, releasing photons of specific energies.
What causes an absorption line spectra
When white light passes through a cool gas, photons of specific energies are absorbed by electrons to promote them to higher energy levels. These wavelengths are removed from the spectrum, resulting in dark lines on a continuous background.
Why are line spectra unique to each element?
Each element has a unique set of energy levels, so the differences between levels—and thus the emitted or absorbed wavelengths—are unique.
how is emission line spectra formed
When an electron absorbs energy and moves to a higher energy level (excited state), it later returns to a lower level, emitting a photon. Each transition emits a photon of a specific energy (and wavelength), forming discrete bright lines on a dark background.
Why do electrons return to the ground state after excitation
The ground state is the most stable, lowest energy state, so electrons spontaneously fall back, releasing energy as photons.
