Diffraction of light question - How do I approach this?

AI Thread Summary
The discussion revolves around a homework problem involving the diffraction of blue light from a star through a grating. The key question is to calculate the number of lines per millimeter on the diffraction grating given the angular separation of the second-order beams. The initial confusion stems from the participant's uncertainty about the relevance of Young's double-slit experiment to diffraction gratings. After some calculations, the participant arrives at a conclusion of 400 lines per millimeter, seeking verification of their working. The response indicates that the principles of diffraction gratings share similarities with the two-slit experiment, particularly in the behavior of maxima.
Micky76
Messages
4
Reaction score
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

  • Fig 5.4.jpg
    Fig 5.4.jpg
    13 KB · Views: 456
Physics news on Phys.org
Read your textbook. It surely mentions diffraction gratings.
 
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.
 
Looks good. With a diffraction grating the only difference is the maxima become sharper otherwise it's the same as the two-slit experiment
 
I multiplied the values first without the error limit. Got 19.38. rounded it off to 2 significant figures since the given data has 2 significant figures. So = 19. For error I used the above formula. It comes out about 1.48. Now my question is. Should I write the answer as 19±1.5 (rounding 1.48 to 2 significant figures) OR should I write it as 19±1. So in short, should the error have same number of significant figures as the mean value or should it have the same number of decimal places as...
Thread 'A cylinder connected to a hanging mass'
Let's declare that for the cylinder, mass = M = 10 kg Radius = R = 4 m For the wall and the floor, Friction coeff = ##\mu## = 0.5 For the hanging mass, mass = m = 11 kg First, we divide the force according to their respective plane (x and y thing, correct me if I'm wrong) and according to which, cylinder or the hanging mass, they're working on. Force on the hanging mass $$mg - T = ma$$ Force(Cylinder) on y $$N_f + f_w - Mg = 0$$ Force(Cylinder) on x $$T + f_f - N_w = Ma$$ There's also...
Back
Top