As implied earlier, microwaves can be produced using an electronic device of the same name. This piece of equipment was discovered within the last century, but the waves themselves are a natural phenomenon. As illustrated in the following diagram they have a wavelength greater than infrared but smaller than radio waves.

Like all waves, microwaves too have a characteristic structure. Important features to note are the crest or peak and the trough. These two terms are important in understanding interference.

Interference refers to what happens when two waves pass through the same region of space at the same time (Giancolli 33). The two types of interference are constructive and destructive. During constructive interference there is greater displacement of the overall amplitude and a wave with higher intensity is created. Oppositely, destructive interference occurs when the two waves oppose one another as they pass, and this causes a reduction of intensity.

Uneven heating occurs when the waves collide with each other as described previously. Similarly, when the troughs and crests of the waves collide, spots that are cooler than normal are created. Likewise, in places where the waves do not collide hot spots appear. This gives evidence that the waves are standing and colliding with each other.

References are to:

Giancoli, Douglas C. Physics: Principles with Applications. New Jersey: Prentice Hall,1998.