Obtain a nine-volt battery, nine-volt battery snap connector, insulated wire, a nine-volt bulb with two terminals, and electrical tape, all of which can be purchased at most electronic or hobby stores. Attach the snap connector to the top of the battery. Connect the red (positive) lead to the positive terminal on the bulb. Cut two lengths of insulated wire about two inches long and strip the insulation off of both ends. Attach one wire to the black (negative) lead from the battery and the other to the negative terminal on the bulb. When connecting the wires and terminals, twist the two together several times and wrap the connections with electrical tape.
First, test the circuit by touching the two open leads together. When touching, the bulb should glow at its normal brightness. Be sure to observe how bright the bulb is for comparison later. Do not leave the leads connected for extended periods of time as this will eventually drain the battery.
Next, touch the open leads to the object you wish to test. If it conducts electricity, the bulb will glow. Objects that do not conduct electricity well (high resistance) may still cause the bulb to glow, but at a much lower intensity.
There are several objects that can be tested for electrical conductivity. Some obvious things to test are different gauges and lengths of wire, coins, copper pipes and nails. Other objects that can be tested can include aluminum foil, water, and door handles. Look for anything around the house that you think may conduct electricity. Test various surfaces of objects and try spacing the leads at varying distances from each other.
Place the leads in a small glass of water and observe how bright the bulb glows. While keeping the leads in the liquid, add a few teaspoons of table salt and slowly stir the solution. Watch as the intensity of the bulb changes intensity. The increasing concentration of salt in the liquid changes the conductivity of the liquid.
Also try cutting a long strip of aluminum foil. Touch the leads at opposite ends of the aluminum foil. Slowly move one lead towards the other, observing how the intensity of the bulb changes with the distance between the leads.