• Support PF! Buy your school textbooks, materials and every day products Here!

Wavelength used in double slit experiment

  • Thread starter songoku
  • Start date
  • #1
1,327
44

Homework Statement:

In two separate double slit experiments, two different wavelengths are used. First wavelength is 708 nm and it is observed the second order bright fringe occurs at same position as third order dark fringe of second wavelength. Determine the second wavelength

Relevant Equations:

Bright fringe: d sin theta = m.lambda

Dark fringe: d sin theta = (m - 1/2).lambda
m × lambda for bright = (m - 1/2) × lambda for dark so:
2 × 708 = 2.5 × second lambda
Second lambda = 566.4 nm

But the answer is 495 nm. Where is my mistake? Thanks
 

Answers and Replies

  • #2
Charles Link
Homework Helper
Insights Author
Gold Member
4,589
1,963
Looks like they did it for 3rd order bright fringe. Did you copy the problem correctly? Looks like they may have made an error.
 
  • Like
Likes songoku
  • #3
34,370
10,446
I agree with your answer. You could round it to 566 nm, however, the original wavelength was not given with more digits either.

708/495 = 1.43 and 495/708 = 0.70 both don't look like plausible fractions and I don't find an easy typo that would lead to this answer.

@Charles Link: That would be 472 nm.
 
  • Like
Likes songoku and Charles Link
  • #4
Charles Link
Homework Helper
Insights Author
Gold Member
4,589
1,963
@mfb has the 472 correctly computed. I should have multiplied it out, instead of estimating it. (495 is not correct for any choice).
 
  • Like
Likes songoku
  • #5
1,327
44
Thank you very much for the help Charles Link and mfb
 
  • Like
Likes Charles Link

Related Threads on Wavelength used in double slit experiment

Replies
1
Views
258
Replies
1
Views
2K
Replies
8
Views
12K
Replies
2
Views
1K
Replies
0
Views
3K
Replies
1
Views
7K
  • Last Post
Replies
2
Views
3K
Replies
5
Views
3K
Replies
3
Views
10K
Top