An electromagnetic wave on a plate? Why not! You cannot eat it, but you can observe it.

After formulating the theory of electromagnetism, James Clerk Maxwell came to a conclusion that the electromagnetic field can exist without charges or current. It should possess the characteristics of a wave. Such fields are called electromagnetic fields. H. R. Hertz, when searching for 'Maxwell's waves' in 1887 used the Ruhmkorff spark coil as the transmitter and some aerials of various shapes. He observed the spark-over with a microscope.

This experiment can be carried out again. We need a piezoelectric gas spark and a small neon bulb. We connect the transmitter aerial made of knitting needles to the spark. The receiver is made of similar wires connected to the neon bulb or a LED. The device is placed on a plate, which provides very good insulation.

We call it "a dessert" experiment, as you need a small plate for it. But it can also be carried out with long hanging wires, as presented on the film on the previous page. The importance of this experiment relies on proving that propagating electromagnetic waves carry not only information (e.g. radio waves) but also energy.

The experiment is easy. One has to remove the metallic cover from the lighter tip, and connect the wires to the two electrodes visible now. The receiver wires are identical to the sender one and are positioned at 5-30 cm distance from it. The wires must be isolated from other bodies, even a wooden table - the ceramic plate is a good isolator. They may also hang vertically on cotton wires, like on the film.

Squeezing the lighter makes the neon lamp in the receiver flash. The light is more intense if a spark appears between the wires of the sender. But the spark is not necessary to make the neon lamp flash; the lamp lights up even if one simply squeezes the piezoelectric lighter, with no spark between the sender wires. The results from this experiment support Maxwell's thesis that variable electric fields (in this case around the sender wires) generate electromagnetic waves.

Currents generated by the piezoelectric lighter are not high, but touching the charged wires (after the lighter has been squeezed) in a rather unpleasant experience.