Light of $λ = 6560A^o$ falls normally on 2cm wide grating. The first order spectrum is produced at $16^o17'$ from normal.

Mumbai university > FE > SEM 2 > Applied Physics II

Marks: 5M

Year: May 2013

Given:

Total width of grating,(w) = 2cm

$λ = 6.56 × 10^{-7}m = 6.56 × 10^{-5}cm$

$θ = 16^o17'$

n = 1

To find:

Total no. of lines (N)

Solution:

For constructive interference

$d sin θ = n λ$

$d sin (16^o17') = (1)(6.56 × 10^{-5})$

$d = 2.339 × 10^{-4} cm$

Now,

$N = \frac{w}{d} = \frac{2}{2.339 × 10^{-4}}$

$N = 8548.39$

i.e $N ≈ 8549$