Firstly, a short definition on the coherence of the waves, two waves(of same type) are said to be coherent if there is a constant phase difference between them (same frequency implied) and of same amplitudes. For e.g. as the following plots shows two waves with a constant phase difference,
Now, Interference is the terms referred to the result of superposing
The waves must be coherent. If the waves that interfere are not coherent, the interference patterns would form but not in definite pattern we would otherwise desire. The waves must approximately have the same amplitude. If the amplitudes varies then neither the constructive nor the destructive interference could occur and the even if it did interefere the pattern may not have sufficient contrast to be observed. Interference can only occur between wave disturbances oscillating in the same plane. For transverse waves, they must be either unpolarized or polarized in the same plane.
If $D>>x$ then, the wavelength($\lambda$) of the monochromatic light is given by,
$$\lambda=\frac{ax}{D}$$
where, $a=$double slit separation in meter($m$), $x=$fringe spacing in meter($m$) and $D=$distance between the slit and the screen in meter($m$).
Here's an explanation of original Thomas Young's experiment,
Here's an explanation of original Thomas Young's experiment,
Examples: A beam of light consisting of wavelenghts 600 nm is
used to obtain interference in Young's Double Slit experiment (YDSE).
Find the fringe separations if the distance between the two
slits is 0.4 mm and screen is placed at a distance of 1.0 m from the
slits. Ans:$1.5mm$
No comments:
Post a Comment