Question

You want to estimate the diameter of a very small circular pinhole that you've made in a piece of aluminum foil. to do so, you shine a red laser pointer (λ = 632 nm) at the hole and observe the diffraction pattern on a screen 3.4 m behind the foil. you measure the width of the central maximum to be 12 mm .

Answer 1

central maximum = d* wavelength/ D
thus
12*10-^3 = 3.4*6.32*10-^7/D
D = 3.4*6.32*10-^7/12*10-^3
D = 1.79*10-^4 m