derive Bragg's equation
Answers
Answer:
A simple way to derive the Bragg equation is as follows.
- The path difference between electrons scattered from adjacent crystal planes is 2d sin θ
- For constructive interference between the two scattered beams the difference must be an integer multiple of electron wavelengths, nλ which gives the Bragg equation.
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W.H.bragg has proposed an equation to explain the relation between inter planar distance (d),wavelength of x-rays (λ)and angle of diffraction of x-rays (θ ) is called Bragg's equation.
First X-ray is diffracted from a point A in the first plane and second X-ray is diffracted from point 'B' in the second plane.
Second X-ray wave travels more distance than first X-ray wave.
The extra distance travelled by second x-ray =CB+BD.
path difference in first & second layer of second x-ray =CB+BD .
If waves of two rays exists in same phase then,path difference is equal to an integral multiple of wavelength of x-rays
Therefore,CB + BD = nλ ..........eq no.1
where, n = 1, 2, 3,...........
In traingle ABC,
sinθ = CB/AB =CB/d
CB=d sinθ............eq no.2
In triangle ABD
sinθ=BD/AB=BD/d
BD= d sinθ...........eq no.3
when equation 2,3 are substituted in equation 1 we get
d sinθ + d sinθ
This relation is known as bragg's equation
where,
n= order of diffraction
θ= angle of diffraction
d= inter planar distance
λ= Wavelength of x-rays.