Electricty generation / MPG

[englishpremier]

Sorry, maybe a daft question, but can anyone tell me why people say that using more electronic devices in the car uses more fuel?

Isn't electricity generated by generated by the movement of a loop of copper wire, between the poles of a magnet?

The speed of the spinning is dictated by the speed of the engine.

With this in mind, how does it make a difference how many electronic devices the car uses?

 

[englishpremier]

It still doesn't make any sense to me. Surely the altenator just spins around some magnets or spins a around a coil. And it spins as the engine is spinning.

This is my understanding of electricity generation. http://www.youtube.com/watch?v=MBMYdE5NQOQ

So imagining that the wand he has in that video moves up and down as the engine spins, then how does it make any difference as to how many devices are plugged in? The wand would always move at the same speed for a given RPM. e.g 100 movements at 1000rpm, 500 movements at 5,000 rpm.

Edit: ok so the alternator rotates a magnet that doesn't touch anything. how is there a slowing force on the engine when it magnet doens't touch anything, so no friction. Surely the pull from the magnet never changes.

 

[englishpremier]

Fair enough. spinning the magnet in the demo generate at school was pretty easy and I didn't feel any resistance no matter how many light bulbs were attached. But I understand the theory. Cheers.