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Old Sep 22nd 2010, 04:29 AM   #1
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single slit diffraction

What happens to the distance between fringes as the width of the single slit become larger? Does the distance between fringes increases? What happens to the centre bright fringe? Does it become larger with an increasing single slit width? My hunch is: Increasing the width increases the size of the bright central fringe, but applets on the net show otherwise. Can someone help?
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Old Sep 22nd 2010, 08:16 AM   #2
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Originally Posted by labview1958 View Post
What happens to the distance between fringes as the width of the single slit become larger? Does the distance between fringes increases? What happens to the centre bright fringe? Does it become larger with an increasing single slit width? My hunch is: Increasing the width increases the size of the bright central fringe, but applets on the net show otherwise. Can someone help?
Without doing any mathematics, my intuition tells me that if you enlarge the width of the slit you'll slowly lose the diffraction pattern and when it is large enough you wouldn't see any diffraction.
From this you can answer to your question "What happens to the distance between fringes as the width of the single slit become larger?"
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Old Sep 24th 2010, 02:41 AM   #3
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single slit diffraction pattern.

Applets on the net show that a larger single slit shows more maxima and minima, thus distance between fringes decreases not increases.
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Old Sep 24th 2010, 02:58 AM   #4
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Angular spread of the central bright fringe is given by

d*sinθ = λ, where d is the slight width. If λ remains same, for larger d, sinθ is smaller. Hence angular spread is smaller.
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Old Sep 24th 2010, 07:23 AM   #5
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Originally Posted by labview1958 View Post
Applets on the net show that a larger single slit shows more maxima and minima, thus distance between fringes decreases not increases.
Yes and it happens when you increases the width of the slit. You are, as I said, losing little by little the diffraction pattern if you increase little by little the width of the slit.
Sarigama gave you a mathematical formula that agrees with the internet applet you found.

If you have 2 minutes of free time, I strongly suggest you to watch YouTube - Quantum Mechanics The Uncertainty Principle Light Particle's. You'll find this video very enlightening regarding your question.
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