Wave Optics- 2 Flashcards
what is meant by intefreferece
Interference is the phenomenon of redistrubution of light energy in a medium on account of superposition of light waves from 2 coherent sources.
the points where the rsultant intensity of light is maximum is called construvtive interference
the pts where the rsultant intensity is minimum is called destructive intetference
what are coherent sources
2 sources of light that continuously emit light of the same wavelength, same frequency with 0 or constant phase difference b/w the 2 is called coherent waves.
2 independent sources cannot be coheren.
This is because light is emitted from individual atoms of the source, when they return to the ground state after being excited by heat or electric discharge.
Since even the smallest source has billions of atoms which cannot emit light in the same phase.
how are coherent sources obtained
coherent sources of light can be obtained from a single light source by using refraction of reflection.
This is because all random phase changes in the parent source are repeated in the image source so the relative phase difference remain constant at all times.
It can be obtained by the division of wavferont or division of amplitude.
conditions of wave fromation
i) coherent source of light must beobtinaed from a single source using rfraction or relection
ii)the light must be monochromatic( single wavelgnth)
iii) Path difference b/w light waves should be small
what are fringes
Interference fringes are the light and dark bands that are produced when two waves interfere with each other
what is fringe width
it is the distance between to alternsating light or dark bands
all dark and bright fringes are of same width
conditions for sustained interference
- 2 light sources must be coherent
- 2 light sources must be narrow
- they must be seperated by only a small distance
-they must be monochromatic
-they should emit light waves of same freq and wavelength continuously
why are soap bubbbles iridiscent in white light
light waves refracting from the opper and lower surfaces of the thin film interfere and hence the condition for bright and dark fringes are satisfied at different positions, for diff wavelength. hence different fringes are produced.
what is diffraction of light
It is the phenomenon of bending of light around the corner of an obstacle in the path of light
on account of this bending, light penetrates into the geometrical shadow of the obstacle.
condition for diffaction
the deviation of light is more pronounced when the dimension of the obstacle is comparable to the wavelength of light,
the phenomenon of diffraction is applicable to all types of waves. it is more pronounced in the case of sound waves/radio waves due to their larger wavelenght.
diffraction at a single slit
It is observed that the intensity has a central
maximum at q = 0 and other secondary maxima at q l
(n+1/2) l/a, which go on becoming weaker and weaker
with increasing n. The minima (zero intensity) are at q l
nl/a, n = ±1, ±2, ±3, ….
No one has ever been able to define the difference between
interference and diffraction satisfactorily. It is just a question
of usage, and there is no specific, important physical difference
between them. The best we can do is, roughly speaking, is to
say that when there are only a few sources, say two interfering
sources, then the result is usually called interference, but if there
is a large number of them, it seems that the word diffraction is
more often used.
Differentiate between interference and diffraction
Interference:
i)Interference is due to the superposition of 2 coherent independent waves.
ii) The width of the fringes of dark and bright bands are the same.
iii) There is a good contrast between dark and bright fringes.
iv) the no of fringes is usually large in number.
Diffraction:
i) Diffraction is due to the superposition of a number of secondary wavelets on the same wavefront.
ii) The width of the bright and dark bands are not the same.
iii) There is poor contrast between the bright and dark bands
iv) The number of fringes are usually less in number.
energy conservation
In interference and diffraction, light energy is redistributed. If it
reduces in one region, producing a dark fringe, it increases in another
region, producing a bright fringe. There is no gain or loss of energy,
which is consistent with the principle of conservation of energy.
