Creating electromagnetic waves.

Equipment and supplies:

• Charged Car battery

• Jumper cables

• Metal file

• Leather or rubber electrical gloves

• AM Radio

• Safety glasses

I present this demonstration after discussing the idea that a changing electric current produces a changing electric field. The changing electric field induces a changing magnetic field. Changing electric and magnetic fields transfer energy away from the source through electromagnetic waves.

Procedure:

Tune your radio to a band with no station and turn up the volume.

Don your gloves and safety glasses.

Connect the jumper cables to the battery.

Connect the free end of the positive cable to the file.

Scrape the free end of the negative cable back and forth across the file.

The radio will receive the broad band electromagnetic waves created. It will sound like strong interference. The frequency of scraping will correspond to the beat of the interference.

Discussion:

Reinforce with your students that all charges have electric fields and that changing the movement of electric fields causes changing magnetic fields and creates waves. Talk to your students about why this is broadband, how the antennae picks up these waves and how this is interpreted as sound.

Further Discussion:

FCC part 15 are the rules and regulations of the US government with regard to broadcasting using the electromagnetic spectrum. These regulations apply to all devices that cause intentional and unintentional interference of the electromagnetic spectrum. Discuss with your students how they might test a new electronic device so that in complies with the rules laid out in FCC part 15. Discuss why a device like a vacuum cleaner can cause interference to your TV and radio but still comply with FCC part 15.