When the adjustable mirror on the Michelson interferometer is moved 20 wavelengths, how many fringe pattern shifts would be counted

The number of  fringe pattern shift is   m  = 40

Explanation:

 From the question we are told that

      The  Michelson interferometer is moved 20 wavelengths i.e  

Generally the distance which the  Michelson interferometer is moved is mathematically represented as

Here is the number of  fringe pattern shift

     So

        m  = 40

the first, second, and fifth options

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