Microwaves have longer wavelength than visible light, and a 20 cm slit is wider than what you would use to observe diffraction from visible light (where the slit would need a width similar to a hair). Microwaves will produce the same type of diffraction pattern as discussed in the background for this Investigation, where the equation

Aballoon is rising vertically upwards at a velocity of 10m/s. when it is at a height of 45m from the ground, a parachute bails out from it. after 3s he opens his parachute and decelerates ata a constant rate 5m/s.when. (a) what was the height of the parachutist above the ground when he opened his parachute? (b)how far is the parachutist from the balloon at t=3s? (c)with what velocity does the parachutist hit the ground? (d)after how long does the parachutist hit the ground after his exist from the balloon?