diffraction!! (1 Viewer)

[mojako]

Can somebody help me pls...?
Which one is occuring in a diffraction of light by diffraction grating and/or of x-rays by a crystal? pls see "which one.bmp" and tell me the correct situation. (the lines there are rays)

If it is the one on the right hand side, can you explain me what's happening in x-ray.bmp? Are the rays reflected and if so, to where?

Thanks !!

 

[Eagles]

diffraction grating.. um, I think its the right one, 'cus it's symmetrical.

the x-ray bmp just shows the structure of crystals(or metals, I'm not sure) and how they get reflected evenly.. hence the lattice structure

 

[mojako]

my point is not about the symmetrical thing (I dont know how to draw symmetrical lines on the left one)
my confusion is:
whether the light goes through the grating or crystal (as in the right diagram) or gets reflected back to the direction where it comes from (as in the left diagram)

and if it passes through the crystal, what is x-ray.bmp showing?
is it that the rays are reflected by certain sets of planes, then the reflected rays get reflected again by another set of planes, and eventually they get out of the crystal as in the right diagram in which one.bmp??

 

[Dash]

my confusion is:
whether the light goes through the grating or crystal (as in the right diagram) or gets reflected back to the direction where it comes from (as in the left diagram)

Ok I haven't done this in a while so... lemme be brief...
A light source will continue to be diffracted, (ie the diagram on the right) until the angle made by the diffraction grating and the light source has reached what we call a 'critical angle'(?) This angle is depended on the type of material that the light is passing through. Once this critical angle has been passed, then light will not pass through and diffract, rather reflect (ie the left diagram)
Hope that made sense

and if it passes through the crystal, what is x-ray.bmp showing?
is it that the rays are reflected by certain sets of planes, then the reflected rays get reflected again by another set of planes, and eventually they get out of the crystal as in the right diagram in which one.bmp??

This example concerns de Broglie's X-Ray diffraction experiment. In a nutshell it just shows how X-ray particles hit the lattice of the crystal and 'bounce' away. It is a somwhat similar concept to the above, but you shouldn't worry about it. Just remember what I've said above... BTW, you're in prelim right?

 

[Tommy_Lamp]

in the first pick its the right one because diffraction occurs evenly
the second pick is an example of bragg diffraction in which they used x-rays to determine the structure of crystals. the rays diffracted off the crystal and they measred the angles, then by using d= lambda/sin theta they determined the distance between the crystal atoms

 

[mojako]

>> A light source will continue to be diffracted, (ie the diagram on the right) until the angle made by the diffraction grating and the light source has reached what we call a 'critical angle'(?) This angle is depended on the type of material that the light is passing through. Once this critical angle has been passed, then light will not pass through and diffract, rather reflect (ie the left diagram)
Hope that made sense <<

Isn't that refraction??
I think diffraction is when waves enter a small hole or aperture, or when part of it waves is blocked by a non-transparent object

In a diffraction grating, are there tiny slits (holes.. where air can pass through) or scratches? My reading so far seems to indicate it can have either one. But this makes me confused.

I'm in yr12.. where did I say Im in prem?

EDIT: now after reading http://www.boredofstudies.org/community/showthread.php?t=36437 I understand diff grating... BUT:
how does x-ray diffraction occur in crystal? Isn't whats happening is just reflection and interference of the reflected waves?
What are the "slits" in a crystal?

 

[Tommy_Lamp]

a diffraction grating consists of a piece of plastic that has been scratched by diamond. these scratches are opaque hence donot allow light to pass through, therefore only the unscratched areas allow light throught. imagine a zebra but instead of black stripes they are opaque

there are no slits in the crystal, the x-ray wavelength is so small that it passes between the atoms. it is diffraction because some light is absorbed and some reflected (i think)

you dont need to go into detail for this point, just need to say that they used x-ray's to dtermine the diffraction angle and hence the distance (see my previous post)

 

[mojako]

>> you dont need to go into detail for this point <<
I know that.. but it doesn't (didn't) make sense for me because the diagram in x-ray.bmp seems to show reflection

textbook should say that (the absorption thing) so that x-ray diff becomes less confusing... at least to me.

Thanks

 

[Tommy_Lamp]

nprbs

 

[mojako]

nprbs

whats that?

 

[Rorix]

t s n prblms wtht vwls nd thr lttrs

 

[mojako]

ok

t s n prblms wtht vwls nd thr lttrs
= to say no problems without vowels and the letters??

 

[mojako]

My Jacaranda book on page 231 (top) says: "A diffraction grating consists of a large number of equidistant parallel lines engraved on a glass or metal surface". If it can be a metal surface, then all light rays will be reflected, so in other words, the process can also be like the left picture in which one.bmp??
That particular paragraph starts by mentioning a diff grating for visible light, and as far as I know of no visible light can pass through a metal.

 

[Rorix]

it is no problems without vowels and three letters i think i was saying....:/