Hey! Sign in to get help with your study questionsNew here? Join for free to post
 You are Here: Home >< Physics

# Physics AS Waves questions

Announcements Posted on
Four hours left to win £100 of Amazon vouchers!! Don't miss out! Take our short survey to enter 24-10-2016
1. I have a few questions regarding the waves (optics) section:

- Why does single slit diffraction cause fringes to be made?, I understand why it is made for 2 slits and the waves and constructively and destructively interfering, but i dont understand why it happens with single slit?

- is single slit diffraction because of interference?

- there was a question in a book that asked: "What happens to the fringe pattern if one of the double slits it blocked completely?" The answer was that there is no fringe pattern, but after blocking 1 slit, why doesn't it just become single slit diffraction?
2. Why does single slit diffraction cause fringes to be made?

Because each point across the slit acts as a single source from which wave fronts propagate. These can then interfere

is single slit diffraction because of interference?

Yes

"What happens to the fringe pattern if one of the double slits it blocked completely?" The answer was that there is no fringe pattern, but after blocking 1 slit, why doesn't it just become single slit diffraction?

If the slit is down to one wavelength there will be no pattern as the first minimum would be at 90 degrees and hence not occur.
3. (Original post by nerak99)
Why does single slit diffraction cause fringes to be made?

Because each point across the slit acts as a single source from which wave fronts propagate. These can then interfere

is single slit diffraction because of interference?

Yes

"What happens to the fringe pattern if one of the double slits it blocked completely?" The answer was that there is no fringe pattern, but after blocking 1 slit, why doesn't it just become single slit diffraction?

If the slit is down to one wavelength there will be no pattern as the first minimum would be at 90 degrees and hence not occur.
thank you

i dont completely understand the last point you made though
4. Essentially, the wider the slit the more points there are to act as sources to interfere with one another. To get a pattern the path length difference to the screen from the different points has to be different by integral numbers of wavelength for a maximum.

With a narrow slit, the sources are closer and hence the points on the screen which have an integral number of wavelength differences will be further apart. Once you are down to a single wavelength width, the angle from the slit to the screen point where one wavelength difference will occur will be 90 degrees. i.e an infinite distance along the screen and hence no pattern.

Hope that is clearer

Write a reply…

Submit reply

## Register

Thanks for posting! You just need to create an account in order to submit the post
1. this can't be left blank
that username has been taken, please choose another Forgotten your password?
2. this can't be left blank
this email is already registered. Forgotten your password?
3. this can't be left blank

6 characters or longer with both numbers and letters is safer

4. this can't be left empty
your full birthday is required
1. Oops, you need to agree to our Ts&Cs to register
2. Slide to join now Processing…

Updated: April 22, 2016
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:
Today on TSR

### Who is getting a uni offer this half term?

Find out which unis are hot off the mark here

### How to get a 1st class degree

Poll
Study resources

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

Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.