Single slit diffraction pattern?

Question

The central bright fringe in a single slit diffraction pattern from light of wavelength 516 nm is 2.3 cm wide on a screen that is 1.05 m from the slit.

(a) How wide is the slit?

(b) How wide are the first two bright fringes on either side of the central bright fringe? (Define the width of a bright fringe as the linear distance from minimum to minimum.)

Answer 1

B. Adjacent minima and noncentral maxima are separated by y ~= λD/a (small angle approximation). Width = separation distance.
A. The central maximum is twice as wide as the noncentral maxima, so y ~= 2λD/a, a ~= 2λD/y