# PHYSICS UNIT 2: OPTICS- DIFFRACTION GRATING

i found this topic really hard to understand, got exam tomorrow, if youre a bit confused about diffraction grating, this is perfect. ive done a document on diffraction grating with diagrams and a worked example at the end! good luck and enjoy :DDD

- Created by: Sally Bradley
- Created on: 24-05-12 21:10

First 245 words of the document:

DIFFRACTION GRATING

Diffraction grating = a system which comprises of a vast number of narrow equally spaced parallel

slits. dSin = n

White light through a diffraction

grating, at each order maximum a

spectrum is formed due to different

colours having different wavelengths.

As red is longest wavelength it will

diffract more than blue, hence why it is

on outside of pattern.

Waves propagating from slits A B C interfere with one another, the

points of constant constructive interference is due to each subsequent wave having moved relative

to the previous one by exactly one wavelength, i.e. have a constant phase relationship. And are

COHERENT

This situation is the same for

greater angles of diffraction,

producing further maximum

orders (constructive interference

fringes)

Further, to calculate the maximum

order (or total number of

diffracted orders seen), = 90,

so dsin90 = n as sin90=1. d=n.

So maximum order, n = d/. For n,

ALWAYS ROUND DOWN (even

if .99!)

Derivation of the equation:

dSin = n

Imagine each order as a right angled triangle:

Where the base is length D (distance from grating

to screen) and height is x (distance between

adjacent orders), the angle = in the main

equation

So for this right angled triangle, tan = x/D

Using this idea, the equation is derived as:

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