Electromagnetic Radiation And Quantum Phenomena Flashcards
Are electromagnetic waves transverse or longitudinal?
Transverse
What phenomenon can be used to show that light behaves as a particle?
The photoelectric effect
Describe the photoelectric effect.
When light above a particular frequency is shone on metal, electrons are released - these released electrons are “photoelectrons”.
What is the threshold frequency?
The minimum frequency of light required for an electron to be emitted.
What equation is used to determine the energy of a photon?
E = hf = hc/frequency
Energy = plank’s constant x frequency
Energy = (PC x 3x 10^8) / wavelength
Why does a photon need to have a minimum frequency in order to live rate an electron?
The energy of the photon is determined by its frequency, the photon’s energy must be greater than the work function in order for an electron to be emitted.
If a photon has a frequency higher than the threshold frequency, what would occur?
The electron will be liberated and the remaining energy is the kinetic energy of the electron
If light is incident on a metal and photoelectric emission does NOT occur, what is the effect of increasing light intensity.
- if it more intense then there would be more photons incident on the metal each second.
- however each photon still carries the same amount of energy as before
- therefore is still does not contain enough energy to liberate an electron
- no effect
What is the photoelectric equation?
Planck’s Constant x frequency = work function + maximum kinetic energy of the photoelectrons
Define the work function
The energy required by an electron to overcome the metallic bond holding it in the metal
What is an electron volt
The kinetic energy of an electron that has been accelerated from rest through a potential difference of 1V
How do you convert electron volts to joules?
X 1.610^ -19
Electron volt (eV). ——————————————->Joules
-:- 1.610^ -19
How does a fluorescent tube work
- High voltage applied across mercury vapour fast moving free electrons which collide with the mercury atoms.
- mercury electrons are excited and then return to the ground state, releasing a UV photon.
- The tube’s phosphorous coating absorbs the UV photons and its electrons are exited, the cascade down the energy levels and emit visible light photons.
What can be used as evidence for the discreet energy levels in atoms?
Line emission and absorption spectra as the lines appear at discrete points which show where a light photon of specific frequency and wavelength has been absorbed or emitted, this shows electrons can only absorb an exact amount of energy to be excited to the next discrete energy level.
What is wave particle duality?
All particle have both particle and wave properties, waves can have properties e.g. light acts like a particle in the photoelectric effect and as a wave when it is diffracted.
