DENJIRO: I have a piece of charcoal here. This can actually become a homemade microphone. I've stacked two pieces of charcoal on top of each other and connected them to a battery. This is going into a mic input. Let's try recording sound onto a cassette tape.
"Happy Energy!"
This is proof that the charcoal is acting as a microphone. This is called a carbon microphone. Let me explain how it works. The resistance of carbon changes depending on the pressure applied to it. If there's light pressure applied, the resistance is low, and the lightbulb doesn't shine too brightly. But if I push down on it to increase pressure, the resistance drops, and the lightbulb shines brightly. With the experiment earlier, the foam that the charcoal was on vibrated due to the vibration of sound. This caused the resistance of the charcoal to change. This difference in resistance is converted into an electric signal.
I have here an old-fashioned telephone. The receiver actually uses a carbon microphone. When I take the cover off, we see some black powder inside. It's powdered carbon. We used this phone's carbon microphone and speaker to perform an experiment outside.
We're going to use a carbon microphone as a telephone. The phone line is 200 meters. "Hello? I hope energy will bring you all happiness." "Our magic word is ‘Happy Energy!'" I heard you loud and clear. It worked!
Normally, there's a need to use an amp to amplify the converted signal that comes out of a mic. But a carbon microphone has the ability to amplify the signal. To prove this, let me bring the carbon microphone up to this speaker. As you can see, we get feedback. The sound coming out of the speaker is picked up by the mic, amplified, then played through the speaker again. The sound keeps getting amplified. Since you don't need an amp with carbon microphones, they were perfect for phones.
I hope energy will bring you all happiness. Our magic word is "Happy Energy!"