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Question
When the width of the slit is made double, how would this affect the size and intensity of the central diffraction band? Justify.
Solution
As the number of point sources increases, their contribution towards intensity also increases. Intensity varies as square of the slit width. Thus, when the width of the slit is made double the original width, intensity will get four times of its original value.
Width of central maximum is given by,
`beta =(2Dlambda)/b`
Where, D = Distance between screen and slit,
λ = Wavelength of the light,
b = Size of slit.
So with the increase in size of slit the width of central maxima decreases. Hence, double the size of the slit would result in half the width of the central maxima
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