Lesson Plan for Modulated Laser Laboratory

Electromagnetic radiation is used in communication. You are more familiar with radiowaves, microwaves, and TV signals. Visible light is also electromagnetic radiation and can be used to transmit a signal. It is a whole new technology called fiber optics. A discussion of this laboratory can be found in the Exploratorium Science Snackbook. We have m

odified the snackbook`s "modulated laser" by substituting an LED (light emitting diode) for a flashlight bulb. By using an LED instead of a flashlight bulb, we can get a cleaner signal. Unlike incandescent light bulbs, the LEDs have a directional polarity. You must connect the positive and negative leads to them correctly, or they will not work. In this laboratory, you will convert sound into electrical pulses. The electrical pulses will be converted into rapid fluctuation in the brightness of a flashlight bulb. This light will be transmitted through the air or fiber optics to a solar cell and converted back into electrical pulses. The electrical pulses will be fed into an amplified speaker and turned back into sound. The apparatus is shown in figure 1. "The induction coil acts as a short circuit for the direct current from the battery. As a result, when the flashlight is turned on, current flows through the coil and the lamp is lit. The induction coil acts as an open circuit for the alternating current from the tape player. As a result, the electrical pulses that would power the headphones must flow through the flashlight bulb. The "sound vibrations" recorded on the tape are transformed into electrical vibrations that produce rapid fluctuation in the brightness of the flashlight bulb. These fluctuations are picked up by the solar cell and are turned into electrical pulses, which are amplified by the speaker or tape...

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