Question
The width of the diffraction band varies
A.
inversely as the wavelength
B.
directly as the width of the slit
C.
directly as the distance between the slit and the screen
D.
inversely as the size of the source from which the slit is illuminated
Answer :
directly as the distance between the slit and the screen
Solution :
The width of the diffraction band is given by
$$\eqalign{
& \beta = \frac{{\lambda D}}{d} \cr
& \Rightarrow \beta \propto \lambda \cr
& \beta \propto D\,\,{\text{and}}\,\,\beta \propto \frac{1}{d} \cr} $$