Question

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

Answer 1

Answer:

The number of bright spot is  m =4

Explanation:

From the question we are told that

    The number of lines is  $s = 500 \ lines / mm = 500 \ lines / 10^{-3} m$

     The wavelength of the laser is  $\lambda = 480 nm = 480 *10^{-9} \ m$

Now the the slit is mathematically evaluated as

        $d = \frac{1}{s} = \frac{1}{500} * 10^{-3} \ m$

Generally the diffraction grating is mathematically represented as

        $dsin\theta = m \lambda$

Here m is the order of fringes (bright fringes) and at maximum m  $\theta = 90^o$

    So

          $\frac{1}{500} * sin (90) = m * (480 *10^{-3})$

=>        $m = 4$

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