Question

Hi I am confused a little about equations for constructive and destructive interference and also about the difference in equations for diffraction and interference and also what equations we use for young's single slit experiment and double slit experiment.Can you please explain the difference??

Answer 1

When two rays of light coming from two coherent sources and meet at a point then we observe interference, if we allow these two rays to fall on a screen then we observe dark and bright fringes alternatively, this is called interference pattern.

constructive interference: when these two rays of light meet at a point in such a way that there is a path difference of zero or integral multiple of then resultant intensity of light is maximum at that point, and we say that these rays interfere constructively or a constructive interference happened at that point.

Destructive interference: when these two rays meat at a point in such a way that there is a path difference of or it's integral then the resultant intensity of light becomes minimum at that point we say that these rays meet destructively at that point or a destructive interference happened.

Diffraction: when a ray of light or wave passes through a sharp edge, it slightly bend from its straight path, this is called diffraction.

For single slit we use diffraction formula:

Where a is width of single slit, is position of minima for m = 1, 2, 3, ... (for minima)

Or

Where y is the position of minima for m=1, 2,3...

For double slit we use formula:

Where d is slit separation and is position of maxima for m = 0, 1,2,3, ....

Or

Where y is the position of maxima​​​​​​ of order me where m=0, 1,2,3 ...