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

# Path Length - AQA Past Paper Question watch

1. I need help on Part A) ii)... Answer is 4λ But I don't undestand Why is it 4λ ...Can anyone explain please..

THank You
2. (Original post by tsrguru)

I need help on Part A) ii)... Answer is 4λ But I don't undestand Why is it 4λ ...Can anyone explain please..

THank You
first the formula for a diffraction grating is given by :

it is said its a second order diffraction grating : so

now to find CE use trignometry
the small triangle ACE..we know AD=2d

can you now use the equations to find CE?
3. (Original post by rbnphlp)
first the formula for a diffraction grating is given by :

it is said its a second order diffraction grating : so

now to find CE use trignometry
the small triangle ACE..we know AD=2d

can you now use the equations to find CE?
Not really, no...

I should had mentioned part a) iii) aswell

a) iii) use your results to show that for the second order image,
4. The "first order" diffraction means there is a path difference of lambda (one wavelength) between B and D. The geometry of the triangles means that the distance between C and E must be 2 lambda. The 2nd order diffraction happens when the distance between B and D is 2 wavelengths. By the same geometry the distance between C and E must be 4 wavelengths.
The reason why the distance must be one wavelength between B and D for 1st order, is that this is the condition for the two adjacent waves to constructively interfere. (A half wavelength difference would mean they destructively interfere.) The interference "fringes" you see in this experiment are areas where the light alternately constructively and destructively interferes to give alternative light and dark lines.
5. (Original post by tsrguru)
Not really, no...

I should had mentioned part a) iii) aswell

a) iii) use your results to show that for the second order image,
Im sorry I should have read the question properly..it says state..Since I did contributed wrongly, here is a website which I came across which looks the topic in quite detail (not that stonebridge's explanation is not good just a alternative one)

Turn on thread page Beta
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 16, 2010
Today on TSR

### Congratulations to Harry and Meghan!

But did you bother to watch?

### Why are girls so attracted to tall guys?

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