9th grade students learn about “The Electromagnetic Spectrum” The electromagnetic spectrum is made up of different types of waves. Microwaves have a wavelength about the size of a housefly. Microwaves reflect off many materials, particularly metals. Radar locates distant objects using the reflective property of microwaves. You may have noticed that the glass door on a microwave oven contains a metal grid. The metal grid reflects the microwaves, preventing them from passing out of the oven.