Turn on thread page Beta
 You are Here: Home >< Physics

# Diffraction Grating watch

1. Hello,
I am currently doing AS physics...
I'm finding it very difficult to understand how a diffraction grating works, and how the rays are parallel, yet their path difference is n*lambda and they somhow overlap...
Could somebody please clarify for me... Thanks in advance
2. (Original post by Ayahhh)
Hello,
I am currently doing AS physics...
I'm finding it very difficult to understand how a diffraction grating works, and how the rays are parallel,
The rays are actually not parallel, they are nearly parallel. This is sometimes called the far-field approximation. They are approximated to be parallel to find the path difference to be d*sin(theta) which is equal to n*lambda.

I will use an analogy. We know that Earth is curved. But the house that you lived in, are the floor curved or flat? In our view, it can be approximated to be flat. But when we view from the outer space, we cannot approximate it to be flat.

(Original post by Ayahhh)
yet their path difference is n*lambda and they somehow overlap...
Could somebody please clarify for me... Thanks in advance
As I mention above, the rays are approximated to be parallel, so they can meet.

Hope it helps.
3. (Original post by Ayahhh)
yet their path difference is n*lambda and they somhow overlap...
Could somebody please clarify for me... Thanks in advance
I forget to address how to arrive the path difference to be n*lambda.

This video gives an intuitive way of finding the path difference.

Another way, is to consider the double-slit constructive interference condition.
4. (Original post by Eimmanuel)

Hope it helps.
Thank you so so so so soo much!!

Turn on thread page Beta

### Related university courses

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: January 11, 2017
Today on TSR

### Exam Jam 2018

Join thousands of students this half term

### Solo - A Star Wars Story

Poll

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE