Mavs04
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Hi, I’m a bit confused about some stuff to do with diffraction:

So my notes say that for single slit interference, the longer the wavelength the less the light diffracts - and that this is why the central maximum gets wider with longer wavelengths. But I’m not sure if this is the reason or if it’s because the waves diffract more and so overlap more - so the interference pattern including the central fringe occurs over a larger area?

But then my notes completely contradict themselves by saying that longer wavelengths are diffracted more/at greater angles and this is why when red light is used for single/double/ diffraction grating interference, red light appears on the outermost edges.
Can someone please tell me which one is correct and explain why?

I’m also a bit confused about how the fringe spacing is related to the angle of diffraction (if at all).

Thanks!
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loubielou123
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This may not help entirely but as I understand it. For a wave to be diffracted the gap has to be comparable to its wavelength. If the wavelength increases it is less comparable so diffracts less, the wave fronts become less curved.
N x wavelength = d sin(angle)
If we consider the central maxima and if d is constant sin( angle) increases as wavelength increases. As sine is at a maximum at 90 degrees the angle of diffraction increases.
Also sin( angle) = x/L where L is the distance to the screen.
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Mavs04
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(Original post by loubielou123)
This may not help entirely but as I understand it. For a wave to be diffracted the gap has to be comparable to its wavelength. If the wavelength increases it is less comparable so diffracts less, the wave fronts become less curved.
N x wavelength = d sin(angle)
If we consider the central maxima and if d is constant sin( angle) increases as wavelength increases. As sine is at a maximum at 90 degrees the angle of diffraction increases.
Also sin( angle) = x/L where L is the distance to the screen.
Thank you is there anyway you could explain that more simply?
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Batchystudies
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Longer wavelength causes more diffraction. I believe the notes you wrote down saying otherwise are incorrect. This means wider central maximum as the photons are spread out more. I'm not definite why longer wavelength causes more diffraction though.
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Mavs04
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(Original post by Batchystudies)
Longer wavelength causes more diffraction. I believe the notes you wrote down saying otherwise are incorrect. This means wider central maximum as the photons are spread out more. I'm not definite why longer wavelength causes more diffraction though.
Ok thank you!!
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