How does an electric Razor works ?

I always had a doubt when I see  my husband shaves his beard with electric razor that ,How does it work? How easily its trimming the hair correctly without causing any damage to skin?There are two different kinds, they are foil and rotary-- but they work the same way.A circle of blades rotates on a springy drive shaft which is powered by an electric motor

The blades on foil razors are enclosed behind very thin steel foils that are perforated. The blades oscillate at extremely high speed and work to lift the facial hair up into the blades to give you that super smooth and close shave. Rotary Electric razors on the other hand have three or four round  revolving or spinning head house cutting blades that spin and cut the hair