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Q105P

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Fundamentals Of Physics
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Short Answer

Show that a grating made up of alternately transparent and opaque strips of equal width eliminates all the even orders of maxima (exceptm=0 ).

It is proved that a grating made up of alternately transparent andopaque strips of equal width eliminates all the even orders of maximaexcept m=0.

See the step by step solution

Step by Step Solution

Step 1: Given data:

There is a grating made up of alternately transparent andopaque strips of equal width.

Step 2: Diffraction from a grating and single slit:

The angular distance θ of the mth order diffraction maxima produced from a grating having line separation d is

dsinθ=mλ .....(1)

Here, is the wavelength of the incident light.

The angular distance θ of the kthorder single slit diffraction minima for slit width a is

asinθ=kλ .....(2)

Step 3:Proof that the even order grating diffraction maximas disappear

Slit separation is the distance between the mid points of two slits. Hence slit separation is equal to twice the slit width, that is

d=2a

Thus, equation (1) becomes

2asinθ=mλ ….. (3)

Subtract twice of equation (2) from equation (3) to get

2asinθ-2asinθ=mλ-2kλm-2kλ=0m=2k2asinθ-2asinθ=mλ-2kλm-2kλ=0m=2k

But

K=±1±2±3

Hence

m=±2,±4,±6

Thus the even order grating diffraction maxima’s (exceptm=0 ) overlap with single slit diffraction minima’s and disappear.

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