A commercial diffraction grating has 500 lines per mm. Part A When a student shines a 480 nm laser through this grating, how many bright spots could be seen on a screen behind the grating

The number of bright spot is  m =4

Explanation:

From the question we are told that

    The number of lines is  

     The wavelength of the laser is  

Now the the slit is mathematically evaluated as

Generally the diffraction grating is mathematically represented as

Here m is the order of fringes (bright fringes) and at maximum m  

    So

=>        

This  implies that the number of bright spot is  m =4

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