Converting mechanical to electrical energy

[MrLobster]

I was watching an experiment that I don't understand. The professor turned a hand crank that generated electricity to light up a bulb. There was also a switch to turn the bulb on and off. When the bulb was on the crank became harder to turn. I don't really understand why that is. Did it somehow create a magnetic force that opposed the motion of the crank?

 

[Astronuc]

I was watching an experiment that I don't understand. The professor turned a hand crank that generated electricity to light up a bulb. There was also a switch to turn the bulb on and off. When the bulb was on the crank became harder to turn. I don't really understand why that is. Did it somehow create a magnetic force that opposed the motion of the crank?

The current created by the changing magnetic force also creates an opposing EMF to the magnetic which created the current.

 

[Mentz114]

Another way to look at it is this - the energy that lights the bulb is being provided by the person turning the crank. If the bulb is off, you have to do less work and the handle turns easily. When the light is on it feels harder because you're working against the back emf created by the flowing current, as Astronuc has said above.