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

Just get a potato it'll be a lot easier to light the bulb that way.

This article may be of help to you:

http://science.howstuffworks.com/electricity3.htm

What kind of "generator" do you mean? An electrical one? And what do you mean by "size"? Watts? Kilograms? Theoretically there is is no minimum size of electrical generator beyond what is practical but commercially there is probably a minimum size of useful generator below which it would be uneconomic to manufacture, because insufficient buyers would want them. Having said that there are small wind powered generators with power outputs of a few watts (I have seen 25 Watt models). Also very small generators are made for for attaching to bicycles to power a white lamp at the front and a red light at the back, usually powered by a little roller which rubs on the back tyre ("tire" in the USA). These are usually 3 or 6 Watts.

Po-ta-to ... po-tah-to, to-ma-to, to-mah-to.

By 'minimum size' I meant minimum volume. I wanna make a working model of science & for that I want one of minimum volume.
Actually I wanna show by that model that mechanichal energy can be converted into electrical energy. So is it really okay to use a generator or should I use any other conversion-method?

A popular type of small generator for bicycles is the "bottle" generator, so-called because of its shape. You might be able to get a used one very cheap or free from a cycle repair shop, and advice about what bulb to use

By definition you will be using a "generator" because that is what a generator does - convert mechanical energy to electrical. Any electric motor can also act as a generator, so you could use one out of e.g. an old model car or similar.

Thanks for help! It was important for me to understand the mechanism of a generator before working on it.

Thanks! I'll consult some teachers about this & will see if I can get it. I'll discuss it later on this thread. . .

As Contrex mentioned above, you just need a small motor. Here is one for $3.50 at Radio Shack. You just have to figure out how to spin it fast enough.

I can't buy that motor because it's out of stock. Its name is "hobby motor", but I think it's not the name formally given to such motors which convert mechanical energy into electrical. Is it?
By the way, the plan has been changed. . .another student in my class is making a similar one. So I just changed the type of mechanism. In a motor it's rotational mechanism, but I want to use a wooden block, on punching which the vibrations get converted into electricity. I'll be thankful if you can help me on that.

The plan has been changed. . .another student in my class is making a similar one. So I just changed the type of mechanism. In a motor it's rotational mechanism, but I want to use a wooden block, on punching which the vibrations get converted into electricity. I'll be thankful if you can help me on that.

"Punching vibrations" like those used in a car engine are converted to electricity by first being converted into rotation. If you want to move a magnet through a coil and create electricity, rotation is the way to go. There is no reason two students can't work on similar projects unless your teacher says otherwise.

As for getting a motor/generator, Radio Shack for example carries lots of these if the one I linked to is out of stock. Just do a search for "hobby motor" or walk into a hobby electronics store and ask.

I talked about it with the guy who's making a similar one, & he said he knew a shop & he could bring a motor for me.
But after knowing that he wanted to cover the motor so that the teacher wouldn't know he was using a motor; I thought that I should, rather than using that motor, create the mechanism of a motor myself. I read about it that one could "roll-a-wire-around-some-rotating-thing" & get electricity. But I didn't really understand the concept. I need it in simple words. Is there any photo or diagram to explain it?

Firstly, if your fellow student covers up the motor up, the teacher will discover it, and your friend will fail the assignment. Your friend needs to understand what the assignment is. Don't have your friend bring you a motor/generator.

Based on your own words, the assignment is to demonstrate how electricity is made by making a very simple generator.

Are you able to read what others have written to you? Several people already have advised you.

Once again, Butrflynet sent you a link that in a simple words with a drawing explains how a generator works:

Can't get much more basic than this

Nil: Does the bulb have to light brightly and can it be LED or other such SS

At least observably glowing. I'll use a bulb of the smallest size.

I understood the theory, but I couldn't understand the relative positions of the magnets, wires & rotating objects needed for it; though now it's clear to me.