This is one of those science fair experiments that are based on a light circuit or an electric circuit. Here you will test how a light circuit is affected by changing a pencil resistor’s length.
Man knew about electricity right from the early days when ancient Greeks produced static electricity by causing friction between amber and fur. Benjamin Franklin risked his life to demonstrate that electricity due to lightning was nothing but static electricity.
In 1800, Alessandro Volta developed the first electric circuit. André Marie Ampère, in 1820, suggested that a correlation existed between magnetism and electricity, a concept that was later established. In 1826, Georg Ohm, who continued the work of Volta, determined that the quantity of electricity that moved through a conductor, its strength and the resistance offered, was directly proportional to the electric current produced, which later came to be known as the Ohm’s Law. We can use these principals in literally hundreds of science fair experiments.
In spite of the groundwork done by Ampère, Volta, and Ohm, electricity was not a useful commodity. The use of electricity became practical for the first time when Thomas Edison invented the light bulb in 1877.
This is one of those science fair experiments where you will make use of the above knowledge established by these great men in the form of cells, circuits, resistors and light bulbs.
- Three wires with alligator clips at both ends
- Battery (9V)
- 9V light bulb (small)
- Bulb holder
- Pencil sharpener
- An extra wire piece
- Popsicle stick
- A coping saw
Setting up the circuit board
All connections must be done using insulated alligator clips. Connect two wires to both the terminals of the battery. Connect the free end of the first wire to the contact screw of a bulb holder and leave the second wire free. Now take a third wire and connect it to the bulb holder’s second contact screw. Leave the free end of the third wire as it is.
Now we have two free ends attached to alligator clips. Now place the light bulb in the bulb holder and touch the free ends of the wires. If the bulb lights up, your circuit is ready. If not, check if all wires are connected correctly.
Making your pencil resistors
Cut various pencils into different sizes such as 3 inches, 5 inches, 7 inches, and so on by using a coping saw. Sharpen each piece at both ends. Please take the help of your parents for this step.
Measuring the pencil resistors
Now using a ruler measure the length of each pencil piece from one lead point to the other. Data must always be accurately recorded in science fair experiments. So, write down the lengths of each pencil piece in a table.
- Now connect each pencil to the circuit one by one. You can do this by clamping both the graphite lead tips of the same pencil with the alligator clips connected to the free ends of the circuit wire.
- Make a note of the brightness of the bulb every time you connect a different pencil resistor to your circuit. Measure the brightness using a number scale. For example, on a 1 to 5 scale, 1 could mean darkness and 5 could mean brightness. Write the rating besides each respective pencil resistor in the table.
- I hope you have not forgotten the extra wire piece and the Popsicle stick. Place each of them in the circuit, rating them in the same way. These serve as the control groups. The extra wire piece is your “positive control” and the Popsicle stick, your “negative control”
I’m sure you like my idea of using your pencil as a resistor. Before you go ahead with it, I would like to offer you a free copy of “Easy Steps to Award-Winning Science Fair Projects”, which you can download from the link below right now.