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Engineering challenge

What can you do to improve this system or explore further?
Khan Academy video wrapper

Some ideas:

Which LED works best? Try several different LEDs and find out which results in the clearest sound or transmits the sound farthest. Does the relative brightness of an LED affect the results?
Cancel the noise. It can be hard to use your system in a room lit by fluorescent lights because the lights flicker on and off, producing an annoying hum. To get rid of the hum, you can make a noise-canceling receiver with two identical solar cells:
1. Hook the solar cells together in a series, attaching the positive side of one to the positive side of the other. Attach the amplifier to the two negative terminals.
2. Shine the light from the LED on only one of the solar cells while the room light shines on them both. The signal from the LED is converted to electricity by one of the cells, and the signal from the room light is converted into electricity by both of the cells. Because the cells are hooked together so that they oppose each other, the two signals from the room light cancel each other out. This allows you to hear the radio signal in a noisy environment.

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