Current direction and the light emitting diode (LED)

Find the light-emitting diodes in your kit. They look like the picture at right. light-emitting diodes

write in your journalWrite a description of the various things the light-emitting diodes do. Here is a list of things to try -- but probably you have done them all already!

The circuit diagram symbol for a L.E.D. is light-emitting diode. The triangle is meant to indicate that current flows only one way, and the curvy arrow is supposed to represent light being made. The bidirectional L.E.Ds (that give different colors for different directions of the current) are actually two diodes in one container.

We have now met several electrical devices (most of them in the section on the direction of current):

light bulb A light bulb turns electrical energy into heat and light no matter which way the current flows.

motor The behavior of a motor does depend on the direction of the current: when you reverse the current, it turns the other way.

buzzer The buzzer in your kit is a very sophisticated device -- there is even a transistor in there -- but fundamentally it also is a kind of electrical magnet. Transistors only work with one direction of current, and so this device is only works when the battery is connected the right way.

light-emitting diode The light emitting diode is a relative of a transistor. Their sensitivity to the direction of the current is inherent to the way they work; when you connect them to a battery the wrong way, no current flows and nothing happens at all.

The light bulb is an example of a "linear" device. It will operate over a wide range of applied voltage; increasing the voltage causes the current to increase, and the light bulb gets brighter. The light emitting diode is a "nonlinear" device: it doesn't do anything at all (and no current flows through it) when the voltage is below 1.6 V; with a higher voltage the current increases rapidly.

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Copyright 2004 J. P. Straley and S. A. Shafer