Quantum Physics Flashcards
What is a PHOTON?
Discrete wave packets of energy.
What is ELECTRON DIFFRACTION?
Path of electron becomes spread out when passing through a spacing comparable to its de broglie wavelength.
What proves the WAVE THEORY of LIGHT?
- When light is shined through a diffraction grating similar to its wavelength, a diffraction pattern occurs with maxima and minima.
- Diffraction only happens in waves.
What proves the PARTICLE THEORY of LIGHT?
- Photoelectrons are only emitted when the frequency of light is high enough to have a high enough energy to overcome work function. Wave theory suggests that light can cause a build-up of energy and cause emission even if the energy of a photon is not large enough to overcome work function in 1 to 1 interaction.
- Photons are absorbed by electrons instantaneously, transferring all their energy.
- Increase in intensity is independent of energy of photon.
Why is CAESIUM used instead of ZINC in a PHOTOELECTRIC EXPERIMENT?
Zinc requires UV which is harmful. Caesium only needs visible light.
What are the MAIN OBSERVATIONS of the PHOTOELECTRIC EFFECT?
- UV light of high intensity causes gold leaf to fall quickly.
- UV light of low intensity causes gold leaf to fall slower than high intensity - less photons incident on plate per second.
- Light source, no matter the intensity, does not cause the gold leaf to fall.
- Metal plate discharges overtime regardless of light incident, so leaf will fall anyway.
- Using a positively charged plate causes no change in gold leaf’s position - Any electrons will be attracted back by positive charge on the surface of the metal plate, even if they are emitted.
- Increasing distance increases intensity, I is proportional to D.
How does an ELECTRON GUN WORK?
- Electrons are accelerated to high speeds due to high supply voltage. KEmax = eV = 1/2*mv^2
- Cathode is placed at negative terminal so the electrons will be repelled or they will be attracted back to the cathode.
- Accelerated electrons pass through graphite with spacing comparable to their de broglie wavelength. wavelength = h/mv
- Electrons are diffracted and emerge to form fluorescent rings with a minima and maxima.
- Wavelength is inversely proportional to v, so if velocity increases wavelength decreases.
- Wavelength = ax/D , wavelength is proportional to x, fringe spacing.
What is DE BROGLIE WAVELENGTH?
All particles have the ability to show wave-like particles if they are moving.
How does the ELECTRON GUN prove ELECTRONS are a PARTICLE?
Electrons have to have a mass in order to be accelerated by the potential difference.
What is an ENERGY LEVEL of an ELECTRON?
- Electrons in an atom have discrete energies.
- When electrons down an energy level, a photon is released.
- When electrons move up an energy level, a photon is absorbed.
- Energy of photon is equal to the difference in energy levels.
What is the gradient of a graph of maximum photoelectron kinetic energy against frequency?
h, planck’s constant.
