Question

When a student shines a 470 nm laser through this grating, how many bright spots could be seen on a screen behind the grating

Answer 1

Answer:

15

Explanation:

Assuming that commercial diffraction grating has 300 lines per mm.

also, given that a 470 nm laser through this grating

d = width of the slit  must be = $\frac{10^{-3}}{300}$

λ = wavelength = 470 nm = 470 x 10^{-9} m

Using the equation

d Sinθ = nλ

n = order

N = number of spots

θ = angle between the diffracted ray and the normal ray= 90°

Assuming the incident ray to be normal to the surface

Plugging the values we get

$3.33\times10^{-6}sin90 = n(470\times10^{-9})$

solving we get

n = 7

Number of spots are given as

N = 2n + 1

N = 2(7) + 1

N = 15