Learning Exercise

Bragg's Law Worksheet

This is a pre-lab activity that students can perform using the Lukin simulation prior to doing a Bragg scattering experiment.
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Exercise

Bragg's Law Worksheet




Introduction


The simulation can be found at the link  http://www.journey.sunysb.edu/ProjectJava/Bragg/home.html
.

Since the simulation has only two rows of "atoms", there are only two
reflected waves interfering.  The applet shows the relative phase
of the incident and reflected waves.  Users can vary the interatomic
spacing d, the wavelength l, and
the grazing angle q. Only angles between
5 deg and 50 deg are permitted.  Clicking on the "Details" button
brings up a meter that shows the intensity of the combined waves. Since
only two waves are combined, the intensity varies smoothly from a maximum
at the angles satisfying Bragg's Law:

2dsinq = ml
(m=1,2,3...)



.


Procedure


Complete the following tables using the given values for each parameter. 
In each case, calculate the value of m from the values for d,
l,
and q.

 






































































Lambda (angstroms)Distance (angstroms)Theta (degrees)Order (m )
2.73.6  
2.525 
 3.235 
3.33.3  
 3.04.5 
 3.611 


For some combinations of d and l in
the table above, there is more than one angle that satisfies Bragg's Law.
Identify these case by determining the other angle(s) that work and calculate
the corresponding value of m in each case. List your answers in
the table below. Note: The number of rows in the table is not equal
to the number of cases.


 































































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Lambda (angstroms)Distance (angstroms)Theta (degress)Order (m)
    
    
    
    
    
    
    
    
   



 

Requirements

Students should be familiar with the conditions required for constructive and destructive interference of waves.

Type of Task

Learning Objectives

To understand the physical orgins of Bragg's law.