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# Young's Slits Problem Watch

1. (Original post by Stonebridge)
x
1. The problem statement, all variables and given/known data

2. Relevant equations

In question.

3. The attempt at a solution

To be clear it's part (vi) that's unclear to me.

In order to ignore the cosine term it has to reduce to 1. This can happen, only if k(x1+x2)/2 = ωt

Is this a correct assumption ?

Also, it is known that k = 2∏/λ and ω=2∏/T

However, I'm trying to think in what way these two components could be equal but I can't get it.

Could someone give me some help, please ?
2. (Original post by Ari Ben Canaan)

In question.

3. The attempt at a solution

To be clear it's part (vi) that's unclear to me.

In order to ignore the cosine term it has to reduce to 1. This can happen, only if k(x1+x2)/2 = ωt

Is this a correct assumption ?

Also, it is known that k = 2∏/λ and ω=2∏/T

However, I'm trying to think in what way these two components could be equal but I can't get it.

Could someone give me some help, please ?
The clue is in the question.
It states that this term can be neglected when considering the pattern on a photographic plate with long exposure.
That 2nd term is time dependent. The first term is only dependent on x1 and x2.
The first term will give the spatial pattern at any time.
The pattern due to the second term is constantly changing with time and averages out of a long period. So the component of the pattern due to the second term would not be seen averaged over a long period.
3. (Original post by Stonebridge)
The clue is in the question.
It states that this term can be neglected when considering the pattern on a photographic plate with long exposure.
That 2nd term is time dependent. The first term is only dependent on x1 and x2.
The first term will give the spatial pattern at any time.
The pattern due to the second term is constantly changing with time and averages out of a long period. So the component of the pattern due to the second term would not be seen averaged over a long period.
I'm sorry to bring this up again, but that last bit in bold, what did you mean exactly ?

In terms of the cosine function what are its special properties as we allow x in cosx to become very large ? Is this connected ?

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