Quantum Flashcards
(9 cards)
What is the stopping potential?
Potential difference needed to stop the fastest moving electrons travelling with Kemax
Explain the process fluorescent tubes
• High voltage accelerates free electrons through mercury vapor.
• Electrons collide with mercury atoms, exciting their electrons to higher energy levels.
• Excited mercury electrons emit UV photons when they return to ground state.
• Phosphor coating absorbs UV, gets excited, and emits visible light as electrons cascade
down energy levels
What is an Emission Spectrum?
A line emission spectrum shows bright lines on a black background.
Each line = a specific wavelength emitted when electrons fall to lower energy levels in an EXCITED gas
What is an Absorption Spectrum?
A line absorption spectrum shows a continuous spectrum with black lines.
These lines correspond to wavelengths absorbed by electrons in a cool gas to move to higher energy levels.
(Think of white light passing a cool gas)
Difference between absorption and emission spectra?
Emission Spectrum
• Excited gas emits photons.
• Bright lines at specific wavelengths.
• Lines show allowed transitions as electrons fall to lower energy levels.
• Black background.
Absorption Spectrum
• White light passes through cool gas.
• Electrons absorb specific photon energies to rise to higher levels.
• Dark lines on a continuous spectrum.
• Lines match up with emission spectrum of same gas.
Wave-Particle Duality Definition
Light and particles (e.g. electrons) show both wave-like and particle-like behavior
• Photoelectric effect: Light acts as particles (photons)
• Electron Diffraction: Electrons behave like waves
What evidence is there to support particles with wave properties?
Electron Diffraction
Light or electrons passing through a narrow gap spread out → this is diffraction
(Electrons are accelerated in a vacuum then pass through graphite crystal leading to
Diffraction → forms a ring pattern = clear proof of wave-like behavior of electrons)
What evidence is there to support waves with particle properties?
Shows light acts as photons in discrete packets of energy
(One photon transfers all its energy to one electron (one-to-one interaction) - can’t be explained using wave theory alone)
Describe de Broglies wavelength and how it proves wave particle duality?
De Broglie shows how wavelength of a particle depends on mv (momentum)
Effect of Momentum on Diffraction Pattern
• Lower momentum (slower electrons) → larger wavelength → wider rings.
• Higher momentum (faster electrons) → shorter wavelength → rings closer together.
• Fits with de Broglie equation: higher velocity → shorter λ.
