# Back-to-School Beginner Science Experiments about Electricity Part 2 – Ohm On the Range

Electricity seems like pretty magical stuff — subatomic force particles found in practically everything. The scientific term for these particles is “electrons,” and for the most part, the technology behind controlling them is very basic. “How basic?” you might ask. So basic that you can show your child how it all works from inside your home. With our Back-to-School Beginner Science Experiments about Electricity series, you and your kids will utilize similar materials and techniques used by Edison, Tesla, and other pioneers of electric energy when they began their experiments over a century ago.

Welcome back! We hope you enjoyed building a lemon battery in our first installment. Before we learn about resistors this week, let’s recap some basic equipment and information.

While most of the materials you’ll need are probably already in your home, you will need a few important things from a home improvement or supply center.

• MultimeterThis device measures AC and DC voltage, amperage, and resistance (ohms). A good, yet inexpensive one costs around \$20 at home centers and can be very handy to have around the house.
• A Pair of Alligator Test Leads.These are wires with little clips at the ends that let you connect circuits.
• A 6-Volt Lantern Battery.These put out a good, safe level of power.

While you won’t be needing to solder any connections in these circuits, you will need to double check that your connections are conducting electricity through them.

PLEASE NOTE: None of these circuits or their components are designed to be plugged into household wall sockets or use household current. They are too weak for that level of power and connecting them to household current is extremely dangerous.

Ohm on the Range!

Just as copper wires conduct electricity easily, resistors limit the amount of electricity that can pass through them. This means you can set up precise circuits using exact amounts of electricity to do all sorts of neat things. You can also make a resistor with a just a piece of paper and a pencil.

Here’s How It Works

1) Use a pencil to draw a really heavy line on the paper. It can be any length your want, but make sure you completely blacken the line with the pencil lead (technically, it’s graphite—a type of carbon that is a semi-metal and an excellent conductor).

2) Next, take your multimeter and set it to 10k Ohms. Put one probe at the one of the line and the other at the far end of the line.

3) While watching the meter, move one of the probe ends towards the other. As the probe points gets closer, the line will start allowing more electricity through to the other probe. The amount of electric resistance is displayed on the mulimeter as Ohms.

4) You’ll notice that, the closer the probes get, the less resistance there will be. This makes it a variable resistor. Variable resistors are used for all sorts of things, including dimming lights, electric motor speed control, and volume knobs.

5) Of course, the line’s resistance also depend on how heavily you’ve drawn the pencil line – thick and heavy conducts better, thin and light will conduct less.

What Can You Do with It?

To test it for yourself, you’ll need your 6-volt lantern battery, a 6-volt flashlight bulb (NOT an LED), and matching socket. Theoretically, you could connect a battery to a light bulb and slide a pair of contact wires up and down the pencil line, raising and lowering the output of the bulb. But our lantern battery is too weak to overcome all the resistance in the pencil line to light the bulb.

So, instead of drawing a line to make resistor, we’re going to use the graphite core inside a pencil to be a resistor.

1) Take two similar #2 pencils. Cut one in two so that one piece is about twice as big as the other.

2) Sharpen both ends of each pencil (or piece) so that you have nice exposed graphite points at each end.

3) Connect one battery test lead to the light bulb socket terminal.

4) Clip the other wire from the light bulb socket onto one of the sharpened point of the shortest pencil.

5) Clip the other wire from the battery to the other sharpened point of the pencil.

6) The light bulb should glow. As you repeat this with longer and longer pencils, you’ll see the bulb glows less brightly.

Be careful to NOT leave your pencil resistor circuits hooked up for too long. Electrical resistance will make the battery terminals get very warm to the touch.

Wow! What did you think about that experiment? Do you have a similar one you want to share? Tell us about it in the comments!

By the Way…

You can check out Part One of our series for more science goodness!

If you’ve had fun with these Beginner Science Experiments, there are hundreds more you and your child can do together to learn even more about electricity. Two classic books that go into better detail about how electricity works are:

Do you have any beginner science experiments you’d like to share with our readers? Tell us about them in the comments!

In Part 3: We’ll learn about magnets, coils, and the power of attraction.