PURPOSE: To demonstrate that energy is transmitted in electromagnetic waves and to show the radiation pattern of the dipole antenna.

DESCRIPTION: The receiving antenna can be moved around in space, keeping the two antennas parallel, to observe the dipole radiation pattern. Rotating the receiving antenna to a vertical orientation (below left) shows that the radiowaves are polarized, as seen by the light going out. Even with the receiving antenna near the minimum of the dipole radiation pattern (below right), the antenna picks up a significant amount of signal.

SUGGESTIONS: Very interesting videos of expanding electromagnetic waves are found at an MIT web site for teaching electromagnetism. See Question of the Week #251 and #252 for information on using this demonstration to enhance class involvement.

REFERENCES: (PIRA 5N10.60)

EQUIPMENT: Radiowave transmitter and dipole antenna with light bulb indicator.

SETUP TIME: 5 min.