What's the minimum size of a generator? (Wanna use it in my science project.)

Thanks! It was a really simple method.

I've thought of something to do with the model. I just need advice about whether this technique is relaible.
I'm thinking of first producing electric current by rotating an axle (by the generator) & then using the current produced to rotate a motor, & the motor directly or indirectly connected to the axle used earlier in such a way that the axle will keep rotating & producing current after the person releases the axle -- & the cycle of energy-conversion continues. A bulb is connected anywhere in the circuit.
Will this technique work for the model? If it will, then how long will the axle keep rotating after human effort on the axle is released?

It seems like you are planning a perpetual motion machine which is not possible. Someone or something is going to have to provide energy into the system for the generator to convert into electricity. It can be a person or a hamster or a battery (although you could just run the light from the battery directly) or a burning flame (if you convert the heat into motion) but it will never run by itself.

Try uranium 235.
That's 'small' and packs an AWESOME punch when refined.

Maybe I didn't explain well. . .the rotating motor will be connected to the axle. The axle will rotate because of the mechanical energy provided by the motor. The motor will keep gaining current from the generator. The generator will keep converting the axle's mechanical energy to electrical energy because the axle will keep rotating because of the energy supplied by the motor, even after the human effort is released.
I know that it'll stop after some time because the energy will be kept losing as sound energy, heat energy, & the energy used to overcome the mechanical friction in the system, but it shall at least work for a noticable period to indicate the concept. . .

The only reason the motor rotates the axle is because it is getting current. The only reason it's getting current is because you're turning the axle. As soon as you stop turning the axle and the axle coasts to a stop, which depends among other things on the bearing friction, everything stops. Whenever you stop supplying energy, everything will start to slow down, usually pretty quickly. You have no storage device in your system to store any excess energy--like a rechargeable battery, so you're proably not going to get more than a couple seconds or so at the most before everything coasts to a stop.

The problem you have is that the losses are a lot higher than you suppose here. Something like this has very poor efficiency so it would stop almost immediately. I also don't think you are really meeting the requirment of the project. The goal is to light a bulb. This is a pretty easy task. A cheap LED, a small hobby motor and a little wire and you are set. You could spin the axle of the little motor with your fingers and light the bulb. If you put a capacitor in the loop to store some energy for a short period and even out the voltage spikes it would work even better.

What if the axle is rotated very fast & the magnetic field in the generator is increased to a very high level (so that maximum input mechanism is converted to current)? Can the bulb glow for 30-40 seconds after the release of human effort?
Please give me any idea of a modification in the system so that the bulb at least glows for 20-30 seconds. . .I can make a very simple project but I want work on this idea of mine.
Please help me.

If you use a large capacitor, yes although I don't know if you can get 30-40 seconds without some design work and investment on your part. Capacitors store energy when there is excess and discharge it when the excess stops. Put a capacitor in parallel with the bulb. You may also need a resistor to slow the rate of discharge from the capacitor. For a bulb, use a LED since they require very little power.

I know it's very easy to make one but I want to innovate.
It's the first time in my life I'm getting a scientific experience like this. I wanna be innovative & make best thing I possibly can.
Please help me. Suggest some modifications in the system so that the bulb lights for at least 30-40 seconds, a time sufficient to highlight my concept.

I've already done that. Use a hobby motor, a capacitor (or a bank of capacitors), a resistor, maybe two. Study basic electricity to see how they should go together and how to size the components. If you want to innovate, you now have to do your homework and figure out how to put those components together. If I do it for you then I am being innovative.

For a gen you can drop a magnet through a coil of wire, whereupon an LED or the like should flicker once

I know how to put them together but I just needed advice to run the system for a longer time.
I've bought the required materials & I'll keep "playing" around with them until I make what I want

Put your capacitors in parallel with each other and your light.

I haven't bought a capacitor yet.
Of what voltage the capacitor(s) should be?
How many should I use?
What's the advantage of using multiple capacitors?
(I've read about a capacitor for the first time.)

Hey soap,u simply ask ur teacher about dis.....or make Virus Generator...

Shouldn't I use you in my project??
An elephant can generate a 100kW power in a single blow which'll be sufficient to power a house of resistors. . .
Don't interfere in my work. . .I know you wanna copy my ideas but I won't let you. . .you creeper!

I've changed my mind. That model would be very inefficient.
I'll make a very simple one now.
A very small fan (of around 3 inch^2) will be powered by some solar cells.
The fan will be enclosed in a structure having only one opening which'll be covered by a table-tennis ball.
When air is blown by the fan, the ball floats in air.
Please help me on that.
The idea is purely mine, but I just need information about the type of solar cells I should use.
Please follow this link -
able2know.org/topic/213848-1

google Edmund Scientific or American Science and Surplus. They have solar kits of various sorts for students. You might want to build some sort of cage around the pingpong ball' otherwise it'll probably fall off to one side or the other whenever it gets lifrted.

I don't think I should buy a kit. . .but now I just need help on some questions. Please follow this link -
able2know.org/topic/213848-1#post-5319452