Quantum Flashcards
(15 cards)
What is the photoelectric effect?
The emission of particles from a metal surface when a light of sufficient frequency is incident on it
What are the key observations of the photoelectric effect?
Threshold frequency-No electrons emitted if frequency is below this value
Instantaneous emission-Electrons emitted as soon as light touches surface
Kinetic energy depends on frequency-Higher frequency=more energetic electrons
One photon is absorbed by one electron
Increased intensity increases emission rate but not electron energy
What is work function?
Minimum energy needed to remove an electron
What is stopping potential?
The voltage required to stop the fasted emitted electron
What is the equation for stopping potential?
(charge of an electron)x(stopping potential)=kinetic energy
What is wave particle duality?
Light and matter act as both waves and particles
What evidence is there for the wave nature of electrons?
Electron Diffraction - Electrons passing through thin graphite produce a diffraction pattern proving wave behavior
What evidence is there for the particle nature of light?
Photoelectric effect - Light interacts as discrete photons
What is excitation?
Electron absorbs energy and moves to a higher level
What is de-excitation?
Electron falls to a lower level, emitting a photon with energy
What is the emission spectrum and what does it show?
Bright lines on a dark background
Shows de-excitation
What is the absorption spectrum and what does it show?
Dark lines on a continuous spectrum
Shows excitation
How does fluorescence work?
They absorb high energy photons(UV) and re-emit them as visible light as lower-energy photons
Why are fluorescent tubes efficient?
Efficient because energy is converted to visible light rather than heat
How do fluorescent tubes work?
This voltage accelerates free electrons through the tube, which collide with the mercury atoms causing them to become ionised, releasing more free electrons.
The free electrons collide with the mercury atoms, causing them to become excited.
When they de-excite they release photons, most of which are in the UV range.
The (phosphorous) fluorescent coating on the inside of the tube, absorbs these UV photons and therefore electrons in the atoms of the coating become excited and de-excite releasing photons of visible light.
