Electronics guys, help me out

[stevel]

Ok, I know this is probably a question for an electronics forum but since I'm not a member of any and I know many of you guys do amp and pedal work and have good electronics knowledge I thought I'd give it a go.

Took my kids to a museum a while back and they had an "efficient" house. One of the displays was a crank you could turn and power a light bulb. There were two bulbs, one standard and one efficient. You could select which one you wanted to turn on. When you chose standard it was MUCH harder to turn the crank to charge it.

A while later our local power company had a display at my son's school and they had a similar thing - hand cranks they were using to show resistance. Now, I get that more resistance makes it harder to crank. I want to know WHY. They couldn't tell me.

So my son gets a snap circuits kit for christmas and in it is a hand crank that you can connect to little circuits to power them - a light for example.

They have an experiment in the book called "hard to crank" and it does what I'm talking about - demonstrates how more resistance makes it harder to turn the crank.

But what I want to know is how the flow of electrons (or resistance to flow of electrons) is manifested physically. I mean, I know that these cranks are basically a coil of wire in some magnets. And there's air between them.

So the only thing I can see is that the magnetic field is some how stronger when there's more resistance. I mean that's the only thing in there that could affect the ability to turn the crank because when there's no wires/circtuits/resistance that crank turns as freely as friction will allow. You attach a wire to both leads on the crank though and suddenly it's much more difficult to turn.

???

Steve

[andrekp]

Sounds like a load of crap to me. A generator is a generator. It doesn't become harder to turn just because its load is more or less efficient. If the generator doesn't create the required current flow, the lamp is dim, or doesn't work. It doesn't affect the resistance of the crank.

[Pete Cage]

The First Law of Thermodynamics would be a good place to start...

[GAD]

When you crank, you create x amount of electricity (keeping it simple). The resistor converts some of that electricity into heat. Thus, you have to crank more (or harder) to create more electricity, so that the end result (including heat loss) is the same as it is without the heat loss (resistor).

The physical difficulty of the crank's ability to turn has nothing to do with this. It may be hard to turn the crank faster due to physical resistance, which is a different thing altogether.

[edit - I'm wrong on the second part - see below]

[19181911]

In other words 100 lbs is heavier than 1 lb, so, it takes 100X the energy it took to lift 1 lb as it does to lift 100.

Or, more output requires more input.

[Old Tele man]

...counter-EMF people! As the 'load' draws more current, it requires more effort to counter that c-EMF induced loading.

[mark norwine]

OTM, for the win.... (again)

[stevel]

Originally Posted by Old Tele man

...counter-EMF people! As the 'load' draws more current, it requires more effort to counter that c-EMF induced loading.

So, in plain English, it's the magnetic field, correct?

Steve

[GAD]

Cool - I learned something!

http://en.wikipedia.org/wiki/Counter...romotive_force

[Sweetfinger]

Originally Posted by andrekp

Sounds like a load of crap to me. A generator is a generator. It doesn't become harder to turn just because its load is more or less efficient. If the generator doesn't create the required current flow, the lamp is dim, or doesn't work. It doesn't affect the resistance of the crank.

You've never used a portable generator on a jobsite, have you?

[Hwoltage]

Someone call Mythbusters (or OldTeleMan)!!

[19181911]

Originally Posted by stevel

So, in plain English, it's the magnetic field, correct?

Steve

Yes, and no. You had to transfer more heat, Remember the first Law of Thermodynamics... "In all cases in which work is produced by the agency of heat, a quantity of heat is consumed which is proportional to the work done; and conversely, by the expenditure of an equal quantity of work (you spinning the crank) an equal quantity of heat (light) is produced."

OK someone correct me, but I'm close

The way a generator makes electricity is in very simple terms (I'm a simple person), spinning a magnet/coil of wire on a shaft inside of a coil of wire/magnet...

So, with the 13 watt lamp your turning the crank at a constant speed and the generator is producing a certain amount of electricity. And, the amount of muscle power you are expending is a set amount.



When you switched to the 100 watt bulb it took aproximately 10 times the effort to turn the crank.

Heat is the source for energy.(1 watt = 3.414 btu per hour) 13 watts is equal to about 44 btu's, plus there is some mechanical loss of heat as well (generator shaft bearings, etc).

100 watts = 341 btu's

So, for the hour that you lit up the 13 watt lamp you expelled enough energy to burn about 12 calories, but to light up the 100 bulb you had to increase the amount muscle power to burn close to 100 calories per hour.

I hated math when I was a kid, but the world revolves around it.

[Pete Cage]

Originally Posted by GAD

Cool - I learned something!

http://en.wikipedia.org/wiki/Counter...romotive_force

No, no, no! You don't understand how TGP works!

Learning is not allowed. You must deny science, refute all well-established laws and principles, misuse tightly-defined terms, and hurl invective at those who have studied these fields.

Get with it, man! You've been warned!

[mark norwine]

Nicely played, Pete...

[andrekp]

Originally Posted by Sweetfinger

You've never used a portable generator on a jobsite, have you?

Thankfully, no I have not.

For the record, my understanding is that If I turn a crank on a hand generator with adequate force to fully light a 13 watt bulb, then I substitute a 100 watt bulb, the mere fact that I changed the load does no affect the difficulty of turning the crank at the same speed, which is a physical effort, not an electrical one.

Now it's true that turning the crank at a 13 watt rate would have no hope of fully lighting a 100 watt bulb, but that's not how I [mis-]understood the question.

Yes, it would take considerably more physical force to light a 100 watt bulb with the same generator, because a generator essentially converts movement into electricity. You need more electricity, you need more movement. And with more movement comes more friction, etc.

But I was answering the question, as I [mis-]understood it as considering whether or not the bulbs fully light as being irrelevant.

If I'm wrong on THAT...well, it wouldn't be the first time...