Young's Double Slit Experiment

1. cupid.callin

1. The problem statement, all variables and given/known data

so here i have shown the distances of two dark fringes ...

from here ... fringe width is $$\frac{\lambda L}{2d}$$
L is distance of screen ... d is distance b/w 2 fringes.

but fringe width is $$\frac{\lambda L}{d}$$ , right ???

What mistake am i making?

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Last edited: May 12, 2011
2. Gregg

462
What's the question?

3. cupid.callin

i wrote it above

by using formula of distance of dark fringe ...

fringe width comes out to be ... $$\frac{\lambda L}{2d}$$

but fringe width is $$\frac{\lambda L}{d}$$

so why am i getting wrong answer

4. cupid.callin

hello ... someone?

The fringe width is the distance between the centres of alternate dark(or bright) fringes.
Lamda D/d as marked on your diagram goes from the centre of a bright fringe to the centre of an adjacent dark fringe in other words you have marked in half the fringe width.

6. cupid.callin

So you mean this is fringe width ??

well this looks satisfying

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You have now marked the fringe width correctly.

8. cupid.callin

are you sure?
because fringe width means "width of 1 fringe"
but (as you said) i have marked width of 2 fringes