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# Phase difference question? Watch

1. Please can you help me out on these two questions, I am stuck on how to do them. Please can you show me your method in solving these two question?
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2. Diffraction grating.pdf (233.3 KB, 82 views)
3. I would like to know the answers too
4. (Original post by Whosthat?)
Please can you help me out on these two questions, I am stuck on how to do them. Please can you show me your method in solving these two question?
Hello there,

The first question implies that you need to be able to recall the values, however I think that a full calculation might be useful to make sense of things.

The diffraction equation states:

As this is the second order image,

With some geometry, we can show that angle is also . As is a right-angled triangle,

The phase difference could therefore be stated as or, in fact, (as is a multiple of and thus represents a whole number of oscillations). This answer makes sense, as these waves should constructively interfere if they are to produce the second order image.

As for the second question, we can say that as is a right-angled triangle,

As we already know the value of (see above),

This also makes sense, as these waves should also constructively interfere.

As I have already said, I believe that the board expect you to learn these values. If you ever get this type of question again, you should be able to recall these. If you have any more questions or think that I have made a mistake, do not hesitate to ask.

Smithenator5000
5. what exam board is this?

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