Re: How can a person be a part of an electrical circuit?

Date: Sat Dec 5 17:24:02 1998
Posted By: William Beaty, Electrical Engineer / Physics explainer / K-6 science textbook content provider
Area of science: Engineering
ID: 911105944.Eg

Message:

Hi Susan!

It actually takes a considerably large electric current to light up even the smallest incandescent light bulb. Those "energy orb" toys are not a simple circuit, instead they contain some sort of transistor amplifier and "blinker" circuit. The circuit is always turned on, but since it normally uses only an incredibly tiny amount of energy, it can last for years without draining its small battery. It measures the electrical conductivity of any object being touched to the silver contacts, and if the object is even slightly conductive, the circuit switches the small flashlight bulb on to full brightness. If you disassemble an "energy orb", look for a blob of hard black glue upon the little circuit board. That's where all the complicated circuitry is usually hidden.

All is not lost. It is possible to (dimly) light some types of LEDs by passing a tiny current across human skin.

SAFETY WARNING:

The following demonstration is fairly safe, but do not use any other power supply except a single 9V battery. AC-powered 9volt transformer supplies are not terribly safe, use only a battery. If you have any cuts or breaks in your skin, don't touch the wires anywhere around that area! Nine volts is far too low a voltage to cause electric shocks in normal circumstances. However, even a 9V battery can become an electrocution hazard if you should electrically connect it to the conductive meat underneath your skin's surface!

Connect a 9-volt battery, a 1000-ohm resistor, and a super-high-brightness red LED, all in series. The LED will light up brightly. Now break the circuit at any point, wet your finger, and touch the two ends of the broken circuit against your skin. The LED will light up very dimly. It only takes a few hundred-thousandths of an ampere to drive the LED. You cannot feel this tiny current. (Works best in a darkened room.)

To light up even the smallest incandescent flashlight bulb, you'd need about four hundredths of an ampere, and this can only be done with high voltage and a painful electric shock!

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