# Help with interference question AH physics? exam tomorrow :(

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1. May 4, 2015

### ah4p

Could someone please explain this question to me I'll include what I thought the answer was and the actual SQA answers.

Please can you read my answer just to see what I'm doing wrong and what I don't understand

It's from the 2009 past paper AH physics

Thanks so much I really appreciate any help exam tomorrow ;(

1. The problem statement, all variables and given/known data

2. Relevant equations

these are gien below in my attampt and in the SQA marking scheme included below

3. The attempt at a solution

this is the answer given by sqa

thanks very very very much

2. May 4, 2015

### BvU

Your 2 n t looks more like 4 n t and what you write down doesn't correspond to what you calculate.

Furthermore, you and sqa both seem to know $\lambda$. We don't.

So: work a little less hasty, and you'll be just fine. Good luck tomorrow !

3. May 4, 2015

### ah4p

sorry λ is 580nm

thanks so much for ur reply