Light of wavelength 520 nm is used to illuminate normally two glass plates 21.1 cm in length that touch at one end and are separated at the other by a wire of radius 0.028 mm. How many bright fringes appear along the total length of the plates.

The number is  

Explanation:

From the question we are told that

      The wavelength is  

       The length of the glass plates is

      The distance between the plates (radius of wire ) =  

   Generally the condition for constructive  interference in a film is mathematically represented as

Where  t is the thickness of the separation between the glass i.e  

    t  = 0 at the edge where the glasses are touching each other and  

     t =  2d at the edge where the glasses are separated by the wire  

   m is the order of the fringe it starts from  0, 1 , 2 ...

So  

=>  

=>    

given that we start counting m from zero

   it means that the number of  bright fringes that would appear is

=>    

=>