Radiofrequency

During our experiment we observe radio waves, these are a type of electromagnetic waves, which propagate in a very wide frequency range, carrying those waves full of information, we convert them into electricity, and then convert them into waves of electromagnetic radiation of the spectrum visible, turning on our LED, which is received by our solar panel, becoming electricity, and then we can hear our light beam.

The battery provides a current to light the LED, if we only had these two components the LED would light up at a fixed brightness. When the music player is turned on, it emits a changing electrical signal through the headphone port, these signals are what makes the headphone speaker vibrate, but here the signal makes the LED blink, the change in brightness happens more 18 times per second.

Most songs have frequencies between 40 Hz and 18,000 Hz, so the flicker will occur too quickly to notice. Then the solar cell receives these flashes, and generates an electrical signal that will vary with the flashing of the LED. This signal is amplified and sent to the speaker, recreating the original sound of the radio.

When you cover the solar panel, it can’t generate the current so there is no sound. Modern communication systems, such as long-distance telephone lines and high-bandwidth communication lines for computers, often use modular light signals. The relatively high frequencies of visual light can carry much more information than low-frequency radio waves. The light used is typically from a laser, not an LED, and the signals are transmitted over a clear fiber optic cable, rather than through the air, but the principle is the same.