IIT JEE , AIEEE Forum - Physics , Modern Physics

jain108

Why would x-rays rather than visible light be used to find the structure of a crystal? Sound waves are used to make images of fetuses in the womb. What would influence the choice of wavelength?

aditya_arora04

Hi,

Look,

In case of visible light, it has much less penetrating power if compared to x rays. Hence, it willl not be able to penetrate inside human body [ because it cannot even penetrate a bunch of papers ]. X rays are better and can penetrate human body very easily and is stopped by bones or human foetus [ once penetrating human tissue it becomes weak and is stopped by foetus tissue ].

So, an exact picture is obtained.

jain108

not satisfied

spideyunlimited

only wavelength of x rays is comparable to atomic distances while light wavelength is much larger.

madmax

X rays have wavelengths comparable to interatomic distances in a crystal lattice.....Hence they provide a much better picture of the structure of Crystals

Rite??
Nudge if helpful

rakesh61

let me tell u a simplified ans only those rays used whose wave length is nearly equal to the inter atomic distance so that diffraction can occour thus can give better strucrture organisation of a crystal

the relation will be help fl

2d sin@ = n lamda
bragg equation

any doubt do ask me

magiclko

Acc to bragg's law, 2dsin x =n

=> sin x /n =

/2d
for a given source and crystal structure,

/2d is always constant (let equal to k)
i.e sin x= nk, whr 'n' is the order of diffraction

now for ur question

n

/2d = sin x
=> n

/2d <1
=> n

<2d
for 1st maxima to take place, n =1 (first order maxima)
=>

<2d
for general crystals, d ~ 3 Angstrom
=>

<6 angstrom
which is only possible for X-rays nd not UV or visible light

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