Question
In a diffraction pattern due to a single slit, how will the angular width of central maximum change, if
a. Orange light is used in place of green light,
b. the screen is moved closer to the slit,
c. the slit width is decreased?
Justify your answer in each case.

Answer

angular width of central maxima of a single slit diffraction is given as $2 \theta=\frac{2 \lambda}{a}$
a. As $\lambda$ increases (orange light has greater wave length) diffraction angle $2 \theta$ will also increase.
b. Increasing or decreasing closeness of screen and slit does not affect angular width.
c. If a (slit width) decreases, $2 \theta$ will increase as $2 \theta \propto \frac{1}{a}$

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