a question about Bragg's experiment

Thread Starter

logicman112

Joined Dec 27, 2008
69
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?
 

Papabravo

Joined Feb 24, 2006
13,749
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?
 

Thread Starter

logicman112

Joined Dec 27, 2008
69
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....
---------------------------------------------------------------------------------------
 
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Thread Starter

logicman112

Joined Dec 27, 2008
69
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?
 

Markd77

Joined Sep 7, 2009
2,806
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.
 

Thread Starter

logicman112

Joined Dec 27, 2008
69
Mark, you are right.
We see the first bright spot in the minimum path difference and the minimum path difference happens when n=1.
 
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