Summary: Many electrical devices use "resistors" in different ways to control the electricity in a circuit. In this experiment, you can make your own resistors out of pencils, and test the effect a resistor has on a circuit.
(Any of The Materials Highlighted in Blue are Clickable Links for Purchasing)
9 V Battery
Automatic Pencil Sharpener
A Coping Saw (you will need your parents help with this)
- Set up your circuit board that you will use to test your resistors.
- Take one wire and attach one end to one terminal of the battery by clipping the alligator clip securely to one of the terminals.
- Attach the other end of that wire to one terminal of the light bulb holder contact screw using the alligator clip.
- Using a new wire, attach one end to the other contact screw of the light bulb holder with the alligator clip.
- Screw the light bulb securely into the light bulb socket.
- Your set up should be similar to the one in this picture:
- Before you start your experiment, you need to make sure your circuit works. Touch the two ends of the empty alligator clips to each other, making sure to hold onto the insulated sleeve so you won't get a shock. Does your light turn on? If it does, move on to the next step. If not, go back to step number 1 and check over your circuit to see if everything is connected correctly.
- Next you will make your pencil resistors to test in your circuit. You will be making several different resistors of different sizes by cutting pencils to different lengths and sharpening both ends of the pencil. You will need your parent's help for this part.
- With your parent's help and using a small coping saw, cut the pencils to different lengths. The pencil lengths for this experiment should offer a nice variety of small to large sizes, and be at regular intervals, such as 2 inches, 4 inches, 6 inches, etc...
- After you cut each pencil, use the pencil sharpener to sharpen both ends of the pencil fragment. Don't worry about changing the lengths of your pencils, because you will be measuring them in the next step.
- Use a ruler to measure each piece of pencil from tip to tip of the sharpened pencil lead. Remember to write down and keep a record of your results!
|Length of Pencil: (measured in cm)
|Brightness of Light: (off, low, medium, high)
- Next, place each pencil resistor one at a time into the circuit between the alligator clips by clipping onto the pencil lead portion at the tip of each end of the pencil. It is important to make sure the clips are attached to the graphite and not to the wood, because wood is an insulator and is not a conductive material.
- Look at the light each time you connect one of your pencil resistors to the circuit. Make a record of your observation, and try to use a number scale to describe what you see. For example, you might use a scale of 1 to 5, where 1 is dark and 5 is bright.
- Remember that piece of wire and that wooden popsicle stick? These are your "control" groups. Put them into your circuit and rate them using the same method and scale you used to test your pencils. The extra piece of wire is the "positive control." The popsicle stick is called a "negative control."