##### Electronics For Kids For Dummies
In scientific terms, radio is the transmission of a certain kind of electromagnetic energy through the air. Electromagnetic energy is energy that is radiated (meaning emitted) by an object and travels in waves, similar to the way sound is transmitted. X-rays, microwaves, visible light, and ultraviolet light (think sunburn) are other types of electromagnetic energy.

One way in which X-rays, microwaves, light, and radio waves differ is in the length of their waves. Picture yourself throwing a rock into a calm lake. When the rock hits the lake, the water on the surface begins to ripple, which means that little waves have been created that emanate in an expanding circle around the center (where the rock hit).

The distance between the peaks of neighboring ripples is the wavelength of the ripple. Different forms of electromagnetic energy are radiated at different wavelengths, which is how you tell them apart.

The frequency of electromagnetic energy is closely related to the wavelength. Frequency is a measure of how many complete up-and-down waves pass a given point in space each second. The longer the wavelength, the lower the frequency, and vice versa.

Commercial radio stations are commonly identified by their transmission frequencies. For instance, 1010 WINS is an AM radio station in New York City. The 1010 in its name refers to 1010 kilohertz (kHz), which is the frequency at which the radio waves are transmitted from the station’s antenna. Another NY-based radio station, 95.5 WPLJ, is an FM station that transmits at 95.5 megahertz (MHz).

The radio frequency (RF) spectrum (that is, range of frequencies) spans 3 kHz to 300 GHz (gigahertz) and is used for TV, shortwave, cellphone, GPS, and other types of transmissions in addition to radio station transmissions. Each AM radio station transmits at a frequency between 535 kHz and 1700 kHz, and each FM radio station transmits at a frequency between 87.5 MHz and 108 MHz.

Radio transmitters send information, which can be music or speech, over RF waves by modifying the pattern of the RF waves in a way that is related to the electrical pattern, or signal, representing the music or speech. This process is known as modulation. The RF waves are carriers of the actual signal (for instance, music). At the receiving end, a radio receiver demodulates the RF waves, separating the signal from the carrier. The signal can then be amplified through an electronic circuit and played through a speaker or headphones.