Background

Bolts of lightning frequently flash across the sky during thunder-storms. Scientific studies of lightning in the late 18th century fostered the beginning of our understanding of electricity. These initial experiments with lightning proved to be very dangerous. After scientists moved their experiments indoors to controlled laboratory environments in the 19th century, the dangers of electric "shocks" were minimized, and rapid progress was made in understanding the nature of electricity. What causes the powerful flashes of light we call lightning? Why do they occur mostly during thunder storms? What is a battery? What is an electric circuit? What happens in an electric circuit to make a bulb glow?

Purpose

1) To investigate what happens when batteries and bulbs are connected in a variety of ways, and to understand what constitutes an electric circuit.

2) To understand the function of a various components in electric circuits.

Materials

Bulbs ($48) (4)	Bulb holders (6)
Battery (1.5 volt) (2)	Bolt (1/4")(1)
Wire (stripped on both ends, 6")(10)	Resistor (various)
Battery holders (2)	Diode
Capacitor (1 Farad)(1)	Steel wool (2" piece)
Clay (small amount)	Light Emitting Diode (LED)
Nichrome wire (2" piece)

1) Arrange a bulb, a battery and a switch as shown at the left, with the bolt in one of the bulb holder sockets. The bolt should act as your "on/off" switch, so make sure that it is functioning properly.

Below is a circuit diagram which uses symbols for various objects in the electric circuit which you assembled above. Study the correspondence between the symbols in the circuit diagram and the actual circuit components.

2) Assemble the circuit shown in the circuit diagram below. What happens to the bulb brightness when the circuit is closed? How does the circuit differ from the circuit above?

3) Study the two circuit diagrams below. Predict the relative bulb brightnesses in each circuit. Test your predictions by assembling the two circuits side-by-side. You may wish to try connecting two batteries in your circuits.

4) The figure below summarizes symbols for various circuit components, most which are in your materials list.

Photographs of the actual circuit components are shown below:

	1.5 volt D-cell battery Switch made from 1/4"x3/4" bolt and a bulb holder		Diode
	Capacitors		Light Emitting Diodes (LED's)

5) Build a "circuit tester" by placing the wad of clay on the table, and brace the two wires from the battery so that the stripped ends exposing the bare wires are not touching anything. (Again, you may wish to use two batteries instead of one.) Explore the function of the various materials provided (e.g. the steel wool, nichrome wire, the diode, the resistors, LED, etc.)

Include in your discussion section a general statement which defines an electric circuit. Also discuss what is meant by a "short" circuit (as opposed to a "closed" or an "open" circuit). Discuss any interesting discoveries you made, such as whether it made a difference which way the battery or any other circuit component was connected into the circuit.

List each circuit component you tested (bulb, capacitor, nichrome wire, steel "wool", resistor, diode, LED), and your comments on how each affected your test circuit.