# Waves Question

• May 18th 2008, 12:56 AM
looi76
Waves Question
Question:
Light from a laser is directed normally at a diffracted grating, as illustrated in the figure below.

The diffraction grating is situated at the center of a circular scale, marked in degrees. The readings on the scale for the second order diffracted beams are $136^o$ and $162^o$.

The wavelength of the laser light is $630nm$.
Calculate the spacing of the slits of the diffraction grating.

Attempt:
$
d\sin\theta = \lambda{n}$

$
\theta = \frac{1}{2}(162 - 136) = 13^o$

$d\sin{13} = {\color{red}2} \times 630 \times 10^{-9}$

$n = 2$ because there are I took 2 reading? or is there another reason?
• May 18th 2008, 01:14 AM
flyingsquirrel
Hi
Quote:

Originally Posted by looi76
The readings on the scale for the second order diffracted beams are $136^o$ and $162^o$.

(...)

$n = 2$ because there are I took 2 reading? or is there another reason?

$n=2$ because $n$ is the diffraction order of the beams and you're using the "second order diffracted beams".