# Homework Help: Diffraction of light waves

1. Mar 15, 2004

### jazzchan

Dear all,

A beam of parrllel light of wavelength 450 nm is incident normally on a diffraction grating with 6000 lines peer cm. Would u give me some idea how to find the maximum number of orders of diffraction thact can be seen on each side of the central (zeroth order) maximuum of the far side of the grating ??

this question only provide the wavelength and the d !! how about the angle ?? Have i need to find the angle first ?? and how to find ??

jazz

2. Mar 15, 2004

### gnome

Maxima occur where there is constructive interference; i.e. where the difference in path length is an integer multiple of the wavelength.

I'm sure you've seen this:

$$d\sin\theta = n\lambda$$

Rearrange it slightly & you can see that maxima occur when

$$\sin \theta = \frac{\lambda}{d} , \frac{2\lambda}{d} , \frac{3\lambda}{d} ...$$

Now, what is the maximum possible value for $$sin \theta$$?