Solve Maximum Number of Fringes Observed from Laser Beam on Grating

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Homework Help Overview

The discussion revolves around a problem in physical optics involving a laser beam incident on a diffraction grating. The original poster seeks to determine the maximum number of observable fringes based on given parameters such as the grating's groove density and the wavelength of the laser light.

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • The original poster attempts to understand the relationship between the variables in the diffraction equation and questions the meaning of certain terms, such as the significance of 'd' and 'N'. Other participants clarify definitions and explore the concept of order in diffraction patterns, discussing the distinction between bright and dark fringes.

Discussion Status

Participants are actively engaging with the concepts, providing clarifications and exploring the implications of the equations. There is a productive exchange regarding the nature of bright and dark fringes, although no consensus has been reached on the interpretation of the original poster's calculations.

Contextual Notes

The original poster expresses confusion regarding the implications of certain parameters and the nature of the observed fringes. There is an ongoing exploration of the definitions and relationships within the context of the problem.

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i would like to ask a que regarding physical optic,so let's nt beating abt the bush,
QUE:A laser beam is incident on a 1.50 x 10^4 grove per inch diffraction grating.The wavelength of the light produced by the laser is 6.30nm and the interference pattern is observed on a screen 2.00m from the grating.Determine maximum number of fringes that can be observed?
here goes the solution but I am nt really clear of the solution:
d sin teta = m X lamda
sin teta=m.lamda.N/l <1
m< l/2N ans is 2.69.
tis is my que,why d=l/N wat does it represents for l/N ?then why do sin teta=m.lamda.N/l <1?why?is it because of polarized light is lesser than 1 while unpolarized light bigger than 1?thanks for your help!:smile:
 
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d is distance between two successive groves, and N is the number of groves per meter.
And sin theta is always <1
 
rl.bhat said:
d is distance between two successive groves, and N is the number of groves per meter.
And sin theta is always <1

oh..ya,thanks a lot,1 more doubt please,what does it mean with 1st order?is that mean a pair of fringe which involves bright and dark fringe?so as the same que as above i asked,so the m value is 2.69..so there are 5 fringes detected,m i wright?2 bright fringes and 2 dark fringes and 1 center max?please tell me if I am wrong?!thanks...
 
When you observe the diffracted along the normal to the grating you see a bright spot. When you move on either side, at a certain angle, again you see bright spots. These are called the first order spots, because the satisfy the relation d*sin(theta) = lambda. If you move still further, again you can see bright spots, which satisfy the condition d*sin(theta) = 2*lambda. These are called second order spots. And so on.
 
rl.bhat said:
When you observe the diffracted along the normal to the grating you see a bright spot. When you move on either side, at a certain angle, again you see bright spots. These are called the first order spots, because the satisfy the relation d*sin(theta) = lambda. If you move still further, again you can see bright spots, which satisfy the condition d*sin(theta) = 2*lambda. These are called second order spots. And so on.

then what about dark spot?is it after at certain angle u observed u saw bright spot at the same time it has dark spot?i;m so sorry for troubling you..:blushing:
 

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