Photoelectric Effect Flashcards
Describe the photoelectric effect
Photoelectrons are emitted from the surface of a metal after light above a certain frequency is shone on it. This certain frequency is different for different metals.
Photo electrons are emitted because electrons near the surface of the metal absorb a photon and gain enough energy to leave the surface.
Photon energy equation
E=hf=ø+Ek(max)
What is the work function
The minimum energy required for electrons to be emitted
Threshold frequency
The minimum frequency of light required to emit photo electrons
What is an electron volt
Unit of energy, usually used to express small energies
What is an electron volt equal to
The kinetic energy of an electron accelerated across a potential difference of 1V or 1.6x10^-19
Convert joules to electron volts
Divide by 1.6x10^-19
Electron volts to joules
Multiply by 1.6x10^-19
The photoelectric effect as evidence of the particle nature of EM radiation
1)wave theory would suggest ANY frequency should cause emission, which is wrong
2)the photoelectric effect is immediate
3)increasing the intensity has no effect of the speed of emission
Why light is a particle
1)one photon interacts with one single electron and all it’s energy is transferred to it.
2)the transfer of energy is immediate
3)intensity is equal to the number of photons released per second
4)all electrons will receive the same amount of energy from a photon of light, however deeper electrons loose energy through collisions when leaving the metal
What happens when an electron gains a certain amount of energy
They move up an energy level (excitation)
What happens after excitation
The electron will quickly return to its original level and release energy in the form of a photon
How can you get a line spectrum
Passing light from a fluorescent tube through a diffraction grating OR prism
What does each line in the light spectrum represent
A different wavelength of light
What is the evidence to show electron in atoms can only transition between discrete energy levels
The light spectrum is not continuous but contains only discrete wavelengths, photons energies must correspond to the wavelengths
