How To Test Which Solids And Liquids Conduct Electrical Current The Best

For an interesting science fair project, kids can test solids and liquids for electrical conductivity. Simple materials include a battery, flashlight bulb, and wire.

Testing solids and liquids for electrical conductivity makes a great science project for kids. In short, substances that are conductors are those that electricity can travel through. Resisters or insulators are those substances that stop the flow of electricity. Many substances fall in between, allowing only a partial flow of electricity.

A simple test for conductivity can be set up using a 6 or 9 volt battery, insulated copper wire, and a flashlight bulb in a socket. For testing liquids, you will also need a medicine cup and some paper clips.

Cut three pieces of the wire each 12 inches long. Scrape the insulation off of an inch on each end of each piece of wire. Wrap the bare wire of one piece around one of the terminals on the battery. Attach the other bare end to the flashlight bulb socket. If you do not have a socket, wrap the bare wire around the base of the bulb. Attach the second wire to the other side of the bulb socket, or wrap it around the base of the bulb. Make sure all your connections are of bare wire.



The final piece of wire is attached to the other terminal on the battery. If you touch the two unattached wire ends to each other, the bulb will light up because the electric current will be complete.

To test materials for conductivity, touch the bare wire ends to the ends of the object. If it conducts electricity well, the light will glow brightly. If it offers some resistance, the light will glow less brightly. If it is an insulator, the light will not glow. For instance, place a fork on the table and touch each end of the fork with the ends of the wires. The light will glow. If you do the same with a plastic fork, it will not glow. Other substances to test include wood, aluminum, glass, rubber, and various types of nails. Keep a chart showing which substances conducted electricity, and which ones produced only a dim light.

A fascinating experiment is making a "rheostat." Rheostats control the flow of electricity in a circuit and are used in dimmer switches. To make a rheostat, split a pencil in half lengthwise exposing the graphite. The graphite must not be broken or split. Touch both ends of the wires to the graphite close to each other but not touching each other. The bulb will glow brightly. Slide the wires farther apart, still touching the graphite, and the light will dim. The graphite does not conduct electricity as well as metals, so the light dims as the electricity is forced through longer distances of graphite.

To test liquids for conductivity of electrical current, attach a paper clip to each loose end of the wires. Attach the paper clips to the sides of the medicine cup and pour the liquid into the cup. If the current is complete, the light will light up. Good liquids to try are water, isopropyl alcohol, and saturated solutions of salt, baking soda, and Epsom salts.

With liquids, you may find that the bulb doesn't light but bubbles can be seen around the paper clips. If you were able to catch those bubbles in test tubes, you could test them and find out that they are hydrogen and oxygen being produced. The electric current is performing the hydrolysis of water, and H2O is becoming H2 and O2! Therefore, the liquid is conducting enough electricity to hydolyze water, but not enough to complete the circuit and light the bulb.

For a more advanced study, you can get a battery operated volt-ohm-current meter from an electronics store or a hardware store. Set it to measure ohms, since this is the unit for measuring resistance.

© High Speed Ventures 2011