Waves 1.4 Flashcards
(11 cards)
Wave-model theories that explain behaviour and properties of light
- Huygen’s Wavelets
- Young’s Fringes
- Fresnel’s Bright spot
- Fraunhofer’s Razor Blades
- Maxwell’s Electromagnetic Waves
- Hertz’s Sparks
- Lenard’s photo-electrons
- Planck’s quantum bundles
Huygen’s Wavelets
Explains propagation of waves, reflection, refraction and diffraction
Each point along plane wave front is tiny source of new small waves
- Have same wavelength and frequency
Young’s Fringes
Light wave interference similar to sound and water waves
Alternating dark and bright fringes produced by double split experiment support wave superposition principle
Fresnel and Poisson’s Bright Spot
Diffraction of light around solid object to produce central spot within shadow region
Fraunhofer’s Razor Blades
Extent of diffraction of light depends on relative sizes of the wavelength and differing aperture
Maxwell’s Electromagnetic Waves
All light is EMR
E/M fields oscillate perpendicularly to each other
Speed of light in a vacuum (3 x 10^8 m/s)
Hertz’s Sparks
Light and radio waves are EMR
Electromagnetic Radiation
All forms of EMR
- Travel at same speed
- Differ only by frequency
Energy carried by EMR proportional to frequency of electromagnetic wave
Photo-Electric Effect
When light above certain frequency (threshold frequency) falls on surface, electrons (photoelectron) emitted from surface
E = h f
Energy increases as intensity and amplitude increases
Energy directly proportional to frequency
Observations of Photo-Electric Effect
- Light must have frequency equal to or above threshold frequency for electrons to be ejected
- Light below threshold frequency will not eject electrons (no matter how intense)
Photoelectric Equation (Assumptions)
- Single proton may initiate ejection of electron
- Certain minimum energy (work function) needed to eject electron from surface
