Width of a narrow slit...?

Question

Light of wavelength 633 nm is incident on a narrow slit. The angle between the first diffraction minimum on one side of the central maximum and the first minimum on the other side is 1.20 degrees. What is the width of the slit?

Answer 1

The angle from normal (center) to each minimum is given by sinø = L/d, where L is the wavelength. The angle between two minima of the same order is twice this. Therefore the width of the slit is L/arcsin(ø/2). This is 6.045*10^-5m