adding a bit of energy at just the right time...
energy not wasted... keeps building up.
good description at
http://scitoys.com/scitoys/scitoys/radio/homemade_radio.html#impedance
also, great descriptions of electrical symbols!! shows what diode DOES... spurts out electricty from one end.
The symbol for the diode looks nothing like the little glass tube with wires coming out. Instead of represeting what the diode looks like, it represents what the diode does.
We can solve both problems by using a trick called resonance.
Resonance is a way of taking a little bit of energy, and using it over and over again, at just the right time, to accomplish a big task. We use resonance when we push someone on a swing. It would take a lot of work to lift someone several feet in the air, but we can do this easily on a swing by giving a little push over and over again at just the right time. Timing is important: if we push at the wrong time, the swing can actually lose energy instead of getting higher.
When an opera singer uses her voice to shatter a wine glass, she is
using resonance. Her voice gives the glass a little push at just the right time, over and over again, until the glass is moving so far that it shatters. In a similar way, we can slosh all the water out of a bathtub by moving a hand in the water at just the right back and forth speed. Each time the hand moves, the water climbs a little higher, until it is over the top of the tub.
Radio waves can act like the sound waves of the singer's voice, or like
the waves in the bathtub. Radio waves can cause electrons to move back and forth in a wire, just like the water in the tub. If the radio waves are moving back and forth at the right frequency, then the electrons in the wire will just be crowding towards one end of the wire when the radio waves start moving them back to the other side. Just like the water in the tub, the electrons will crowd higher and higher at the ends of the wire. These electrons can do work, like moving the brass disk in the earphone to create sound.
