A 100 watt bulb will normally glow brighter than a 50 watt bulb as long as you are comparing similar style bulbs. You have to compare Incandescents to Incandescents, Fluorescent to Fluorescent, LED...
Yes it can but it is a bit more complicated then that. The motor that is rated at 100 Watts will draw 100 watts electrical power, but will only output 70-80% of that in mechanical power. So in order...
Using a voltage regulator (LM78XX come to mind), or through Pulse Width Modulation. In the first case, the typical output power will be at 4W tops (LM78XX are typically rated at around 1A of...