True, alternating current varies with time. That is what defines AC. In the USA it alternates sixty times per second. A light bulb's filament does fluctuate slightly in output intensity sixty times every second. But, you don't see it because it happens so fast! The same applies to an electric fan: you may study how an AC motor works. The fan does NOT convert the AC to DC. The end result is the fan appears to us to be blowing at a steady, fixed rate.
Old-fashioned TV sets had a "refresh rate" which meant the picture was being displayed once, erased, and then displayed again...at over thirty times per second. Your eye's persistence made it seem continuous. A spinning disc with a slot cut out of it allowed us to "stop action" this refresh rate.