Superposition Flashcards
What is coherence
Two sources are said to be coherent if waves from each source have a constant phase difference between them ( must have same frequency)
What is interference
It refers to the results of the superposition of 2 or more waves of the same kind. The displacement of the resultant wave is given by the principle of superposition
What is constructive interference
Occurs when 2 or more waves meet in phase and superpose to produce a resultant wave of maximum amplitude
What is destructive interference
Occurs when 2 or more waves meet anti-phase and superpose to produce a resultant wave of minimum amplitude
What is path difference
Path difference is the difference in the distance travelled by 2 waves from their respective coherent wave sources to a point
Expressed in terms of a number of wavelengths
What is the condition for constructive interference
Path difference = nλ where n = 0,1,2,3,4,….
What is the condition for destructive interference
path difference = (n + 1/2)λ where n = 0,1,2,3,…..
What is diffraction
it is the spreading of waves around an obstacle or through a gap into its geometrical shadow
What are the conditions needed for observable interference pattern
- Waves must be of the same kind and superpose at a point
- The waves must be coherent
- The waves must have about the same amplitude
- For transverse waves, they mut be un polarised or have the same plane of polarisation
Why does the Young double slit experiment have a double slit
The 2 slits serve as a pair of coherent light sources because waves emerging from them originate from the same wavefront and therefore maintain a constant phase difference.
How is the fringe separation x related to the wavelength λ of the source, screen distance D and double-slit separation a?
x = λD/a
- Valid only if a «_space;D and for fringes close to central maximum
What is the angle θ of the first minima for single slit diffraction
sinθ = λ/b
- b is slit width
What is resolving power
The resolving power of an imaging system is its ability to produce 2 separate distinguishable images of 2 separate object. It depends on wavelength from objects, how close they are to each other and how far away they are from observer
What is the Rayleigh Criterion for resolution of 2 patterns
When the central maximum of the diffraction pattern from one source is directly over the first minimum of the diffraction pattern from the second source, the patterns are just distinguishable
What is the Rayleigh criterion for resolving power of a single aperture of diameter b for small θ
θ = λ/b
