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Course: Exploratorium > Unit 4
Lesson 3: Turn Light into Sound- Light into sound introduction
- Materials and tools
- Build and test the receiver
- Build the transmitter
- Construct the parallel circuit, put it all together
- What's going on: Turning sound into light
- Engineering challenge
- Turn light into sound: Complete activity guide
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Build the transmitter
The electrical signal from a radio is converted to light with the help of a 9V battery. Created by Exploratorium.
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Why does an LED have to be hooked up a certain way? Is this different than normal lights?(0 votes)
An LED is a light emitting diode and as with all diodes they will only conduct in one direction (called the forward direction). They have two terminals - the anode and the cathode. To conduct the anode has to be connected to the positive connection of the supply and the cathode to the negative supply connection.(8 votes)
Is this schematic correct? I have been trying to build this transmitter for the past few days to no avail. The circuit works without the radio, but the light goes out when I connect the radio. What am I doing wrong?(2 votes)
Why would the 470 ohm resistor be the side where the electrons ... have already left the light ... and are moving back to the battery ... you would think the resistor needs to be "on the way" to the light .. to prevent it from burning out.(2 votes)- I have a question, must we use a radio only for the sound transmission, because I have set up the circuit, having to change the schematic so that the resistor was on the positive side, because the circuit wasn't working otherwise, and when I connect the monoaural positive and negative wires to the paper clips, the led turns off, any idea as to how? And does it have to do with the fact that I'm not using a radio? Because the circuit works just fine before I put on the monoaural wires to the paperclips.(2 votes)
- At1:30into the video, the instructor indicates that the positive lead from the battery (red) goes thru' the resistor and into the LED.
However,the circuit diagram shows the positive terminal as as connecting straight into the LED.
Why this apparent difference between the circuit diagram and what the instructor indicates?
Great experiment !(1 vote) 
Do I need an AM / FM radio for this experiment, or will a computer or smartphone work?(1 vote)
Instead of using the resistor if we could use a battery of 3V or lower potential, can the
problem of burning of the LED be fixed?(1 vote)- If sound energy is transmitted into light then why do we have to use an external source of energy (battery) ?(1 vote)
is this project expensive? its sometimes hard to get my hand on extra cash if its a high price it is was it is but you know...(1 vote)
@2:22he says that the electrons are "leaving" the negative terminal and essentially traveling through the circuit. This is really bothering me because I am watching many online videos and am hearing two different things. Most videos explain it like this one, that the electrons themselves are moving through the circuit.
The other videos however say that the electrons themselves don't move but PUSH electrons into other electrons, Like if I had a long broomstick and I pushed at one end, the other end would push too, but the electrons remain with their original atoms.
Can somebody please clear up for me what the electrons are really doing. Are they staying with their original atoms or are they physically flying through electric wires hopping on the backs of different atoms. Thank you!(1 vote)
1:30Video transcript
- [Voiceover] Now we have to
build our light transmitter. It's gonna take the electrical
signal from the radio and turn it into a time
varying light signal. So here's the circuit diagram. We have the radio and it has
two leads coming from it. And let me show you that. So here's the radio and here is, once again,
the mono phono plug. It's got the one band on it. It will just work with
anything you plug it into. So I'll plug that into the radio and that goes to two leads... which will connect to
the rest of our circuit. Now in that circuit there's
going to be a nine volt battery, which has a positive and a negative side, and a 470 ohm resistor. If I don't have that 470 ohm resistor when I connect the nine volt battery to my light emitting diode, the light emitting diode
will burn out instantly so we need that resistor. Now, the nine volt battery snaps into this battery holder. I use Velcro to hold it
in place on my breadboard. And the battery holder is color-coded. The positive terminal of the battery goes into the red lead
on the battery holder. So this red lead is the positive terminal and it goes out and it
connects to one side of the light emitting diode, and the black lead goes to the other side of the light emitting diode. Now, my switch is simply an alligator clip that I clipped to a bent paper clip, and that's how I turn my light emitting diode on and off. Now, there's a little bit of a trickiness about light emitting diodes. A light emitting diode has two legs to it, a long leg and a short leg. And the longer leg must be connected to the positive terminal of the battery to make the light emitting diode glow. So when I mounted my light emitting diode to my circuit, I made sure the longer
leg went to the red lead on the battery. Now, what's going on
here is that electrons are actually leaving the
negative terminal of the battery, going through the black wire, going to the short lead of
the light emitting diode, and they come in with the full
nine volts, very high energy, and they drop their energy
and turn it into light. And then the electrons with lower energy continue around back into the battery.