Wave-Particle Duality and Quantum Theory Flashcards
What is a Transverse Wave?
When vibrations are perpendicular to the direct of propagation
What are 4 Wave behaviours?
Reflection, Refraction, Diffraction and Interference
What is Reflection?
When Light Bounces off an Object
What is Refraction?
The bending of light as it passes from one medium into another
What is Diffraction?
The spreading out of waves as it passes through holes or around corners
When does maximum diffraction occur?
When the hole equals the size of the wavelength. The diffraction increases as the hole decreases of the wavelength increases.
What is interference?
The net effect of the combination of 2+ waves interacting.
What is super-positioning?
The combination of 2+ waves in the same location.
What is Huygens Principle?
It states that each point of a wavefront can be a source of secondary wavelets.
How does Huygens principle explain diffraction?
Every part of a wavefront would spread out in all directions but most of the wavefront is blocked by the material. The part not interfered with is able to spread out, creating diffraction.
What is path difference?
Path difference is the difference in the physical distance between the two sources to the observer.
What is constructive and destructive interference?
Constructive is when waves are in phase. Destructive is when the waves are 180 degrees out of phase.
What are 3 reasons that Light is a wave?
- Diffraction (Double Split and Diffraction Grating)
- Interferenance (Double Split)
- Polarization
What are 3 reasons Light is a particle?
- Compton Scattering
- Photoelectric Effect
- Photon absorption and emission (Bohr’s Model)
What are 2 thing that undermine light’s wave model?
- The Ultraviolet Catastrophe
- Michelson-Morely experiment (search for the aether)
Explain how young’s double slit works and how it proves light is a wave.
- Light is a transverse electromagnetic wave
- When light lands on the double split a pattern of light and dark spots are created
- This can be explained through diffraction. As the wave moves through the 2 slits it creates 2 new wavefronts that interfere with each other
- Constructive interference = light spots
- Destructive interference = dark spots
- This proves light is a wave as is demonstrates properties of interference and diffraction
Explain diffraction grating and how it proves light is a wave.
- Diffraction grating is optical elements that disperse light composed of different wavelengths
- Colours travel at different velocities resulting in different wavelengths
- As the colours travel through different mediums it disperse differently
- This proves light is a wave as it demonstrates properties of diffraction
Explain polarization and how it proves light is a wave.
- When a transverse wave is only allowed to vibrate in one direction
As light can be polarized it proves it is a wave.
What is unpolarized light?
Light that consists of a collection of waves that are polarized in different directions
Explain how the Michelson Morley experiment creates issues in the Wave model prediction of light.
- It was an experiment to search for the ‘aether’ an invisible medium used for transporting waves.
- It was predicted that light would travel slower in one direction that the other
- The experiment was conducted by reflecting a beam of light on mirrors (partially coated in silver) that was split and predicted to return to the original point at different times.
- No change was measured and therefore it was proven there was no aether
- As waves require a medium this caused issues in the wave model for light.
Explain the Ultraviolet Catastrophe and how it creates issues in the wave model of light.
- Black bodies are theoretical objects that can only emit and absorb radiation but not reflect it
- As radiation is absorbed temperature is increased creating different colours as photons of different frequencies are emitted.
- The scientists made a rule for the temperature of the object and the colour of light it would emit. This rule caused Ultraviolet light to be in infinite amounts.
- Then plac came along and quantised the energies, modeling the theory to the reality
What is the photoelectric effect and how does it work to prove light is a particle?
- The ejection of electrons from a metal plate when light falls on it
- Light is a quantised particle, a photon
- The energy of a photon is E=hf where the E is used to liberate the electron from the atom (W)
- When photons collide either all/no energy is transferred
- Ek = Excess energy
- Intensity = increases #photons (Photons below the threshold frequency didn’t carry sufficient energy regardless of intensity)
What is Bohr’s Model and how does it work to prove light is a particle
- Electrons move in circular orbits
- The bigger the radius the greater the energy
- Only particular energies have stable orbits
- When an electron moves from higher to lower energies, quantised energy is emitted (photons)
Explain emission and absorption spectra
As an electron moves up shells it absorbs a photon or a certain colour of light. As it moves down it emits a photon, creating a spectra.
- Emission spectra: Hot gas (Absorbs and releases energy)
- Absorption spectra: Cold gas (Absorbs energy)
