C13 (Quantum Physics) Flashcards
Einstein proposed that although light exhibits wave-like properties, it travelled…
It travelled in particles called photons
Photons contain discrete “energy packets” called..
Quanta
The energy of each quanta depends on what?
Depends on the frequency of the light
What has the development of quantum physics led to
Understanding how we can use different models to describe EM radiation
E.g use the photon model to explain how EM radiation interacts with matter, and the wave model to explain its propagation through space.
The energy of each photon is directly proportional to what
To its frequency
Equation for the energy of a photon
E= hf
h- planks constant (6.63x10^-34)
The general speed of a wave through a vacuum
3x10^8
Equation for energy of a photon (mixed with the wave speed equation)
E= hc / lamdar
Energy of photon is inversely proportional to
Wavelength
Instead of using joules we often use another unit when measuring energies at a quantum scale
The electron volt (eV)
1 eV is equal to what
1.60x10^-19
Electrical energy equation
Ee=eV
How can you work out planks constant
Do a simple experiment with LEDs to determine a value for the plank constant by considering the energies of the photons they emit.
What is photon electric emission
The release of an electron when a photon of light hits the metal surface the electron is on.
Ultra violet light causes the zinc to emit electrons (releases more than visible light as it has a shorter wavelength and a higher frequency, and therefore more energy).
Work function
The amount of energy needed to release an electron from a metal
(Generally, work functions are lower for more reactive metals).
Photon energy equation (involving work function)
Photon energy= work function + KE of electron
Equation for work function (when KE=0)
E= work function = h x fo
fo (min freq required to release an electron)
Equation for max KE
Ek= hf -work function Ek= hf - hfo
Conclusions for photoelectric effect (4):
- For given metal no photon electrons are emitted if the radiation has a frequency below a certain value (the threshold frequency).
- The maximum KE of photoelectrons is unaffected by the intensity of radiation
- The number of photoelectrons emitted is proportional to the intensity
- The max KE of photoelectrons increases with the frequency of the radiation
Wave properties of particles (what did De Broglie suggest):
De Broglie suggested that all particles could behave as waves. He deduced that a particle has a wavelength, and it was dependent on only the momentum of the particle.
De Broglie equation
Wavelength = h / p = h / mv
Evidence of wave like properties of light
Diffracts
Refracts
Reflects
Polarisation
Evidence of particle like properties for light
Photoelectric effect
Reflection
