How Many Bright Fringes Appear on the Screen in a Diffraction Experiment?

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Homework Help Overview

The discussion revolves around a diffraction experiment involving a grating with 600 lines/mm and light of wavelength 500nm. The original poster seeks to determine how many bright fringes appear on a screen located 2.0m behind the grating.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • The original poster attempts to calculate the number of bright fringes based on angular separation and total angle considerations. Some participants question how to find the highest order fringe visible on the screen and the relationship between the angle and the order of the fringe.

Discussion Status

Participants are exploring different aspects of the problem, with some offering hints about relevant equations. There is a focus on understanding how to determine the maximum order of fringes that can be observed, but no consensus has been reached on the approach to take.

Contextual Notes

There is a mention of the need to consider the maximum angle for visibility on the screen, indicating that assumptions about the setup may be under discussion.

bigsaucy
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A diffraction grating with 600 lines/mm is illuminated with light of wavelength 500nm. A very wide viewing screen is 2.0m behind the grating.

b.) How many bright fringes can be seen on the screen.

MY ATTEMPT:

i worked out the angular separation between bright fringes to be 0.305 rad (i know this is right because i got the answer to part a right). So then the screen has a total angle of 180 degrees or pi rad. therefore i reasoned that the number of fringes is pi rad/0.305 rad. But since there won't be any bright fringe at 0 rad or pi rad, the final solution must be pi (rad/0.305 rad - 2)

Is this reasoning correct or am I completely off? (Note, the answer is 7 fringes)
 
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Hint: What's the highest order fringe visible on the screen?
 
Yeah... still not hitting any switches, sorry, lol.
How are we meant to find the number of orders?
 
What equation tells you the angle that a bright fringe makes?
 
d sin theta = m lambda?
 
bigsaucy said:
d sin theta = m lambda?
Exactly. Use that to find the greatest value of m that can appear on screen.
 
I don;t get it? How am I meant to solve for something that has two unknown variables? the theta and the m value?
 
bigsaucy said:
I don;t get it? How am I meant to solve for something that has two unknown variables? the theta and the m value?
Ah, but theta is not an unknown. What's the largest angle that a fringe could make and still be visible on the screen? (For all practical purposes.)
 

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