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

Diffraction of light question - How do I approach this?

  • Thread starter Micky76
  • Start date
  • #1
4
0

Homework Statement


Question:
Blue light of wavelength 485.6nm from a star is incident normally on a diffraction grating. The light is diffracted into a number of beams, as shown in Fig 5.4.(attached)

The angular separation of the two second-order beams is 45.72 degrees.
Calculate the number of lines per millimetre on the grating.

Homework Equations



The Attempt at a Solution



I genuinely do not know where to start the question. I know the formula for Young's double slit experiment however this does not seem to relate to it at all. Any suggestions for starting the question would be really appreciated.
 

Attachments

Answers and Replies

  • #2
vela
Staff Emeritus
Science Advisor
Homework Helper
Education Advisor
14,632
1,268
Read your textbook. It surely mentions diffraction gratings.
 
  • #3
4
0
Never seen the formula before. The question is from an old past paper so it might be off the specification. The only thing relating to path difference that I have seen is the Young's modulus experiment. Anyways I had an attempt, is my working correct?

Θ = 45.72/2 = 22.86 degrees
2*485.6*10^-9 = d sin(22.86)
d = 2.50*10^-6 m
d = 2.50*10^-3 mm
N = 1/d = 1/(2.50*10^-3) = 400
Lines per mm = 400

There is no mark scheme for this so if someone could verify my working that would be great.
 
  • #4
vela
Staff Emeritus
Science Advisor
Homework Helper
Education Advisor
14,632
1,268
Looks good. With a diffraction grating the only difference is the maxima become sharper otherwise it's the same as the two-slit experiment
 

Related Threads on Diffraction of light question - How do I approach this?

  • Last Post
Replies
5
Views
3K
  • Last Post
Replies
4
Views
2K
  • Last Post
Replies
3
Views
2K
Replies
5
Views
3K
  • Last Post
Replies
3
Views
3K
Replies
12
Views
1K
  • Last Post
Replies
2
Views
3K
  • Last Post
Replies
2
Views
1K
Replies
3
Views
1K
Replies
12
Views
545
Top