UFO Ball
An electronic circuit that can bring everyone together.

Concepts
Electronic circuits, conduction

Materials
  • UFO ball
  • Wire – about 5 cm long
  • Paper – a strip cut about 2.5 cm by 5 cm
  • For Extension: another wire and substances to test such as paper, aluminum foil, cup of water, cup of oil, etc.

Introducing the Activity
Discuss with the class how electronic circuits work, focusing on how electricity must travel in a complete loop or circle. If any part of the circle is broken electricity won’t flow. The UFO ball is an incomplete electronic circle. By touch the two metal electrodes with a substance that conducts electricity the circle is completed and the ball lights up and makes noise. Touch a metal wire across the electrodes to demonstrate how it works.

Note: don’t touch the electrodes with your hands during the demo; let it be a surprise!

Procedure (for small groups)
For each number students should record their observations.
  1. Touch the wire against one of the metal electrodes of the ball; then touch the wire across both metal electrodes of the ball.
  2. Touch the paper strip against one of the metal electrodes of the ball; then touch the paper strip across both metal electrodes of the ball.
  3. Touch one of the electrodes with your finger; then touch both electrodes with your fingers.
  4. Have one person touch one electrode. Have another person touch the other electrode. Then have both people with their free hand touch hands.

Procedure (whole class)
  1. 1. Everyone in the class needs to form a circle and join hands.
  2. 2. Two people in the circle should release their hands and touch one of the electrodes on the UFO ball.
  3. 3. Have the two people touching the UFO ball continue to do so while other members of the class, one pair at a time, release their hands momentarily and then join hands back together again.

Drawing Conclusions
Summarize the following:
  • Which objects conduct electricity?
  • Which objects did not conduct electricity?
  • Make an inference that tries to explain why some objects conduct electricity and others do not.
  • For materials that did cause the UFO ball to work, what way did you have to connect them? Why was it important to connect them this way?
  • Are you a conductor or an insulator? Explain how you know.

Extension
  • Connect two wires to the electrodes of the UFO ball so they are perpendicular to the surface of the ball but parallel to one another. It is important that the wires do not touch. Touch each wire with your hands to ensure a good connection (the UFO ball should light up and make noise). If necessary, tape can be used to connect the wires to the electrodes.
  • Have students touch the two wires to different substances to see if they are conductors are insulators. Good materials to use include aluminum foil, paper, cardboard, spoon (stainless steel).
  • Students can also test different liquids to see if they conduct electricity. Good liquids to test include tap water, distilled water, vegetable oil, and soda.

Note: it is important that the UFO ball not be submerged in any of the liquids.

figure17.jpg
Figure 17: Two wires attached to the UFO ball turn it into a conductor detector. Here it lights up and makes sound when the two wires come in contact with aluminum foil.
Explanation
For electricity to flow it must do so in a complete circle, or circuit. When electricity flows in a circle it never “backs up” or “doubles back”. It goes in one way and out a different way. Any path along which electrons can flow is a circuit. For a continuous flow of electrons there must be no gaps. A gap is usually provided by an electric switch that can be opened or closed to either cut off or allow electron flow. Most circuits have more than one device that receives electrical energy. These devices are commonly connected in a circuit in one of two ways, series or parallel. When connected in series, they form a single pathway for electron flow. When connected in parallel, they form branches, each of which is a separate path for the flow of electrons. Both series and parallel connections have their own distinctive characteristics.

The UFO ball is an incomplete electronic circuit which consists of a battery, LED (light emitting diode), speaker and an IC (integrated circuit). What makes it incomplete is the fact the circuit is not connected until the gap between the two metal electrodes on the outside is bridged by a conducting material. When this occurs electricity can flow from the battery to the LED and the IC, simultaneously creating light and sound. The gap between the electrodes is acting as an electric switch. The battery is generally a button battery, e.g., LR 41 and sometimes there are two of them connected in series. The LR 41 button battery creates 1.5 Volts of electric push and two of them in series create 3V of electric push. The LED is a generally red in color and is connected in parallel to the IC which creates the sound which is amplified by the speaker. Since the LED and IC are connected in parallel if one of them breaks or is the other one will still function. Except for the speaker, the electronic components discussed above are mounted on a printed circuit board (PCB) which consists of a dielectric material (an insulator) and conducting pathways (typically copper). The speaker is a quarter-sized disk found under the PCB.

Materials can be classified as conductors, insulators or semiconductors. Conductors such as copper, aluminum, brass and steel allow electricity and heat to pass freely through them. Insulators such as oxygen, rubber, wood and plastic do not allow electricity and heat to pass freely through them. Semiconductors such as silicon and germanium have behaviors between conductors and insulators. Sometimes it is said that semiconductors have average conductivity, not as good as a conductor but not as bad as an insulator, but more often semiconductors act as insulators who become conductors under certain situations.


figure18.jpg
Figure 18: Inside the UFO ball is an electronic circuit.

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