Wave Nature of Light
Wave Nature of Light
Wave Nature of Light
http://physicsstudio.indstate.edu/java/physlets/java/slitdiffr/index.html
The fringe pattern formed by a single slit consists of Alternate bright and dark fringes and the fringes fade away from the centre.
Diffraction Patterns
Youngs experiment
http://www.matter.org.uk/schools/Content/Interference/doubleslits_1.html
http://www.walter-fendt.de/ph11e/interference.htm
Coherent Sources
Coherent sources are those which emit light waves of the same wavelength or frequency and are always in phase with each other or have a constant phase difference.
Polarization
The wave disturbance have the same polarization.
Amplitudes
The two sets of wave must have roughly equal amplitude.
Path Difference
The path difference between the light waves must not be too great.
If the source slit is moved nearer to the double slits the separation of the fringes is unaffected but their brightness increases. If the separation of the double slits decreases, the separation of the fringes increases. If the width of slits is widened, the number of fringes decreases. If white light is used the central fringe is white and the fringes on either side are coloured.
http://webphysics.davidson.edu/physlet_resources/bu_semester2/c26_thinfilm.html
Constructive interference occurs if the path difference between the two reflected light beams is
1 ( n ) 2
Where n = 0, 1, 2,
Destructive interference occurs if the path difference between the two reflected light beams is
Where n = 0, 1, 2,
On the other hand, the part reflected at the lower surface must travel the extra distance of 2 t, where t is the thickness of the film. That is, 2t is the path difference between the two reflected beams. If 2t = (n+) then constructive interference occurs. If 2t = n then destructive interference occurs. When t is large, several values of satisfy the equation. The film will appear to be generally illuminated.
The process of coating a film on the lens is called blooming. A very thin coating on the lens surface can reduce reflections of light considerably.
http://users.erols.com/renau/thinfilm.html
http://www3.ltu.edu/~s_schneider/physlets/main/thinfilm.shtml
Light rays reflected from the upper and lower surfaces of a thin wedge of air interfere to produce bright and dark fringes. The fringes are equally spaced and parallel to the thin end of the wedge.
http://www.gg.caltech.edu/~zhukov/applets/film/applet.html
Fringe Spacing, y
tan
2 tan
When a curved glass surface is placed in contact with a flat glass surface, a series of concentric rings is seen when illuminated from above by monochromatic light. These are called Newtons rings.
Newtons rings are due to interference between rays reflected by the top and bottom surfaces of the very thin air gap between the two pieces of glass. Newtons rings represent a system of contour fringes with radial symmetry. The point of contact of the two glass surfaces is dark, which tells us the two rays must be completely out of phase.
Flatness of Surfaces
Observed fringes for a wedged-shaped air film between two glass plates that are not flat. Each dark fringe corresponds to a region of equal thickness in the film. Between two adjacent fringes the change in thickness is /2. where is the refractive index of the film.
Three-slit pattern
The fringes of the double slit pattern fade away from centre and disappear at the single slit minimum.
There is a subsidiary maximum between the double slit maxima.The fringes become narrower and sharper.
http://www.matter.org.uk/schools/Content/Interference/gratings.html
The fringes become sharper as the number of slits is increased. The subsidiary maxima become less and less significant as the number of slits is increased.
http://www.matter.org.uk/schools/Content/Interference/gratingExplored.html
Diffraction Grating
A large number of equally spaced parallel slits is called a diffraction grating. A diffraction grating can be thought of as an optical component that has tiny grooves cut into it. The grooves are cut so small that their measurements approach the wave length of light.
Diffraction Gratings
A diffraction grating splits a plane wave into a number of subsidiary waves which can be brought together to form an interference pattern.
d Path difference = d sin
If d is the slit spacing then the path difference between the light rays X and Y = d sin . For principal maxima, d sin = n. The closer the slits, the more widely spaced are the diffracted beams. The longer the wavelength of light used, the more widely spaced are the diffracted beams.
n=2
2
Since sin 1,
n 1 d
n=1 n=0
1 1 2
n=1
n=2
The highest order number is given by the value of d/ rounded down to the nearest whole number.
A spectrometer is a device to measure wavelengths of light accurately using diffraction grating to separate.
Turntable Collimator C Light source Achromatic lenses Cross-wire Diffraction grating
Telescope T Eyepiece
Eye
Spectrum of a star
- Procyon