Interference Flashcards
What is interference
When two waves are traveling at the same space or medium at the same time, they produce a combine resultant displacement of the two waves according to the principleof superposition
What is the principle of superposition
When two or more low energy waves are supposed on the same space or medium, the waves travel independently through each other and the resultant displacement at each position is the algebraic sum of the displacement due to each wave
What are the conditions for interference to produce observeable interference
Both waves must have nearly the same frequency
Both waves much have equal or nearly equal amplitudes
When would constructive interference take place and what would happen to the wave
Two waves have to be in phase (crest alligned)
Summation of both waves
- resultant amplitude equals to sum of the two component amplitudes
When would destructuve interferance take place
Two waves have to be out of phae (by 1/2 a wavelength)
The amplitude of waves cancel out each other
What is a ripple tank and what does it show
Two vibrators are hooked together in ripple tank
A circular wave travels out from each vibrator, the waves travel independently through each other, constructive and destructive interferance observed
Destructive interfence position known as node, combination of node regions result in straight lines at point far away from two sources
Wha is Young’s double split experiment
Runs sunlight thr a single pinhole and have the light illuminate onto double pinholes (now uses slit instead of pinholes)
Done to ensure the mutual coherence of light thr both pinhole, similar direction, amplitude and phase
Demonstrates light was a wave
What is the interfernce effect observed during Young’s double slit experiment
Fixed wavelength
- fringes wider when slit closer (easier to see)
- fringes narrower when slits are further (harder to see)
Fixed slit separation
- fringes wider for longer wavelength
What does thin film interference result from
Due to multiple reflection process
- a single ray will reflelct multiple times in a thin film which results in phase change at reflection forming color fringes
When would phase change occur
Phase changes at reflection
- ONLY the ray reflected from front surface of thin film will undergo phase change
Must be light travelling from lower to higher index, this phase change result in destructive interference
What happens if light travels from higher index
No phase change occurs, results in constructive interference
(refracted ray)
How thickness affects phase change
When film too thick, phenomenon of multiple reflection will not occur
What is the undesirble effects of thin film on lens
Constructive interference from reflected
Destructive intereferce from transmitted
What is the typical thickness of thin film and why is it adjusted
1/4 of wavelength to limit the amt that light can travel before it undergoes reflection n refraction
(ensures desireable effects: reflected = destructive, transmitted= constructive)
What does AR coating do to lens
Reduce the amount of reflection by destructive interference
Increase the transmission of the lens by constructive interference
