2*d sin(teta) = n * lambda
This is the formula of Bragg. How can we measure 'n'?
An important fact which no physic book wants to talk about!!
'n' is the order of the reflected beam, what does it mean? How we can measure it?

 

If none of 'em talks how did u know abt it?

 

Notice the second condition: - http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/bragg.html

 

Do you mean this?

Bragg's Law

*************

Curses! Beenthere and moved on!

 

Wiki (http://en.wikipedia.org/wiki/Bragg's_Law) says: "n is an integer"!!
It is very ridiculous!! We want to know what is n exactly? We know that it an integer!!
The following link seems broken:
http://hyperphysics.phy-astr.gsu.edu...tum/bragg.html

 

Your mistake is the expectation that there is a single solution -- there isn't. The statement that "n is an integer" just means that there may be multiple solutions depending on the wavelength of the light and the geometry of the crystal lattice. Why are you being so obstreperous anyway?

 

as stated above, there are many solutions.
every time 2*d*sin(theta) equals an integer multiple of the wavelength, you see a bright spot. ie. you see a whole set of bright spots, equally spaced apart.

similar to this:
http://en.wikipedia.org/wiki/File:Single_slit_and_double_slit2.jpg
(slightly different math, but same idea of coherent interference from regularly spaced sources/reflection)

 

I thought Bragg's experiment can measure the wavelength. So it can not!!
Because there are two variables unknown, n and the wavelength!!

So why the following extract from a famous physic book states that William Bragg invented this theory to measure wavelength?
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In 1913, William Bragg and his son Lawrence, proposed a simple method of
measuring the wavelengths of X-rays by means of their ‘reflection’ from crystal planes.
Crystals comprise atoms (or ions) that are arranged in a spatial lattice, such that they....
---------------------------------------------------------------------------------------

 

Please add your comments then I will let you know something which has never been mentioned in physic books. How 'n' can be measured in Bragg's experiment logically?

 

Am I missing something? I'd have thought you increase the angle from zero until you see a patch of X-rays. That means n=1. The next patch is n=2, etc.
I imagine you see X-rays at angle = 0 because they go through the sample - ignore that.

 

Mark, you are right.
We see the first bright spot in the minimum path difference and the minimum path difference happens when n=1.