Quantum Physics Flashcards
What is quantum?
Discrete packets of EM radiation
What is the equation for the energy of 1 photon
E=hf
What is the equation for the energy of 1 photon when there is no frequency
hc/λ
The higher the frequency of Em radiation…
The more energy the wave packets carry
Do photons have charge?
Photons do not have charge
What is the definition of electron volt
The kinetic energy gained by an electron when it is accelerated through a potential difference of 1 volt
What is the equation for work function
φ = hf
Work function = Planck constant x threshold frequency
how to demonstrate the photoelectric effect
clean zinc plate mounted on the cap of a gold-leaf electroscope. Plate initially charged negatively
A u-v lamp shining on plate
gold leaf collapses as electrons emitted from plate when
ultra-violet light is incident on the zinc plate
so experiment indicates the emission of negative charge
describe photoelectric effect in terms of the phyiscs of quantum behaviour
1 photons are absorbed by 1 electron in the metal surface.
electrons must have absorbed sufficient energy to overcome the work function energy of the metal
photons with energies above
the work function energy will cause photoelectron emission
Number of electrons emitted also depends on light intensity
State the difference between electron and photons
- electrons have mass, photons have zero mass
3.electrons have charge, photons are uncharged
5.photons travel at speed of light
Describe Einstein’s theory to explain the photoelectric observations
Individual photons are absorbed by individual electrons (in the metal surface
Only photon with energy above the work function energy will cause photoelectron emission/idea of threshold frequency
Photon energy is proportional to frequency
hf -ф = KEmax is the equation resulting from conservation of energy or resulting from the meaning of each term
A wave model does not explain instantaneous emission
Explain why electron can be emitted form a clean metal surface illuminated with bright ultra violet light but never when infrared light is used
Energy of infrared is less the. Work function of the metal
Electrons can behave as a wave.
Describe the behaviour of electrons that demonstrates that they have wave properties.
• electrons may be diffracted by crystal lattice
• to produce circular interference fringes
• diffraction of electrons occurs when the wavelength is comparable similar to the gap size
changes in the electron’s speed/energy change the size of the interference fringe spacing
electrons have a (de Broglie) wavelength
Pattern in rings be side atoms in crystal lattice irregularly arranged
