Pencil Resistor question

[kthiry]

We are trying to see a difference in the brightness of a light bulb by attaching alligator clips from an insulated alligator clip set to a 9V battery and using different size pencils (sharpened at both ends) to show how electricity can travel through the lead of the pencil. With each size pencil, the light bulb looks the same brightness each time we change the pencil to the different sizes. How can we make this work?

[deleted-71785]

kthiry,

I am very new to the forums. I am not familiar with which science project you may be attempting since I have not had a chance to read them all yet. One thing that I have done and I know works well and is easy to control, is drawing various size rectangles of different lengths and widths on a plain white sheet of paper (completely filling them in). Touch your alligator clips to opposite ends of the rectangle. You might have to make very long rectangle(s) (dark lines) or short more square drawing; I'll leave the exploration for you. You could also try other shapes as well.
You may want to experiment with different kinds of pencils or maybe even pens and other objects (tin foil cut to different lengths comes to mind).

It might be a good idea when working with any kind of battery to be wearing safety glasses. While the chance is very small there is still the possibility that if a 9V battery shorts you could get an eye injury (not to scare you but its good practice when working electronics).

Regards,

-Vince