A simple technique to make a variable resistor from paper and pencil.

Step 1: List of Materials Required:

All the things required to make this resistor are readily available in homes and
you will not require to spend any money to buy them.
The materials required are as follows:
(1) A thick (rather stiff) sheet of paper.
(2) A HB pencil.(preferably 3B,4B or 6B)
(3) A ruler or scale.
(4) Few metal paper clips.(will be used as the pins of the resistor)
(5) A multimeter or ohm meter to measure the resistance and calibrate your
resistor.
(6) pair of scissors.

Step 2: Lets Make It !!!

Building this resistor will hardly take an hour.You can build it in just 5 steps.
Step (1):
SubSteps:
(1)First take the sheet of paper(as i have told before it should be stiff and rough).
(2)Cut a small strip out of it.(as I have shown in the picture).

Step 3: Start Scribbling !!!!

Now take out the heck out of the pencil ! This is was is the second step.
Step (2)
Substeps:
(1) Take a scale/ruler and your HB pencil and place the ruler near one side(the lenght i.e. the longer side) of the strip at about 0.5cm.
(2) Draw a demarker line with the ruler
(3) Now rub and scribble your pencil in the demarked area (as hard as you can !!).

*It is better if you scribble in a linear way ,horizontally and carefully seeing that no space is left blank in that area.

*If you use here a thin paper then it will tear off so I again recommend to use a stiff paper.

Step 4: Time to Work Seriously!!

This is the most important part of this instructable - THE CALIBRATION PART.
Before starting with this part,
PLEASE MAKE SURE THAT:

the area beyond the demarked one (where we have scribbled) is clean as while scribbling you have may have touched the other part of the paper,so rub off the ajoining area with an eraser-neatly!

*make sure that your multimeter is working and set your multimeter to to the resistance range of 200K ohms.

Step (3):
Substeps:
(1) Put the clip to the starting point of your strip(i.e. on the most lefthand side).
(2) See to it that the clip is firmly put (as shown in the figure)
(3) Next to this clip, put another clip ,leaving a space of around 1/2 to 1 cm.
(4) Connect your multimeter probes to the clip and check the resistnance.
(5) Adjust the position of the second clip to get the desired resistance.
(6) After getting the desired resistance ,see that the clip is frimly stuck.
(7) I have made actually here a variable capacitor like taht used in a light dimmer , so you can see in the photo that i have stuck two clips as the other pin of the resistor . The clips as so calibrated that the resistance difference between two clips is of 10 k ohms.You can calibrate many clips side by side with specific resistance interval and can make your own light dimmer !!

Step 5: Limitations,Experimentation and Applications -

Though this resistor is modest at perfromance it can't be used for all practical applications.This is because it is difficult to calibrate this resistor to lower resistance value in ohms.Also while making a PCB it would be difficult to attach it.But for experimental purposes it is good.You can learn a lot about resistors by this instructable.The pencil lead is actually a graphite rod (carbon).By rubbing it on paper you transfer the carbon particles on to the paper.The paper is a insulator.The comibantion of paper and carbon acts as a resistor.You can tryby using a very thin line of pencil on the paper to thick lines on the paper and see the difference in calibrating it and its effect on resistance.You can use it to make a "light dimmer" or controlling volume output in a sound circuit or to control motor speed etc.It can also be used in small circuit or circuits in which it is hard to find the required resistance.

I hope you liked my first instructable.If you have any suggestions or comments or questions you can tell me freely in the comment space or can email me at science4u@gawab.com