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### Course: Exploratorium>Unit 4

Lesson 3: Turn Light into Sound

# Build the transmitter

The electrical signal from a radio is converted to light with the help of a 9V battery. Created by Exploratorium.

## Want to join the conversation?

• Why does an LED have to be hooked up a certain way? Is this different than normal lights?
• 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.
• 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?
• 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.
• 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.
• At into 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)
• @ he 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)