Can You Hear Me Now?
Turn on a portable radio, tune it to a station, then place the radio in a metal mesh trash can, and remove your hand. The radio reception will drop out and you will hear static.
Touch the radio with your hand and the reception will come back. Remove your hand and you'll only hear static again.
Reach in and hold your hand near the radio, without touching it, and the reception will return!
The metal enclosure acts as a Faraday cage, shielding the interior from the radio waves outside. It would also shield the outside from radio waves transmitted from inside the cage. This is why signals are sometimes blocked inside elevators, and it is also how RFID blocking wallets work.
- a small portable radio
- a metal trash can
This one doesn't involve any assembly, you just have to have the right items on hand. If the trash can has been used for trash, you can put a fresh bin liner inside before you put the radio in.
Radio waves are essentially the same thing as visible light. Why can you see through the mesh of the trash can but radio waves don't go through?
You can try to similarly block other types of communication: wifi, bluetooth, cell phone signals. Experiment with other types of metal enclosures, and see if you can figure out why some of them do or don't block different kinds of signal.