Electric guitars come in a massive variety of shapes, sizes, styles and prices. Over the years they have been available in 6, 7, 8, 10 and 12 string varieties and (and Keith Richards from the Rolling Stones has also famously resorted to a 5 string guitar by removing one string from his Fender Telecaster). They come with one neck, double neck, can be fretless, and now we even have digital guitars...it's endless.
In general they use magnetic pickups located on the body, under the strings, which capture the vibration of the metal strings. This signal is then passed through tone and volume controls, out through the output socket and into an amplifier, which errr, amplifies the sound of the vibrating strings.
Tip for newbies. You do not plug an electric guitar into the socket on the wall. Really. You plug it into a Guitar Amplifier (which in turn gets plugged into the wall socket). Just so you know ;-)
The solid body electric came to prominence in the 50's, but the ground work had already been done as early as the 1920's as a solution for guitarists to be heard over the din of drums and brass in showbands and Jazz bands. At that stage guitarists were still using acoustic guitars which projected the sound from the soundhole. The first electric's were simply acoustic guitars (and specifically large bodied Jazz style guitars) modified with the addition of an electromagnetic pickup.
Over time, manufacturers realized that they could just stick these pickups on a solid slab of wood rather than an intricately built, large, hollow bodied guitar and since then the shapes and styles have been coming fast.
Having said that, some of the very first solid body guitar shapes are still the most popular guitar shapes by far, for example, the Fender Stratocaster and Telecaster, and the Gibson Les Paul. In fact I would suggest that 99% of electric guitars available today are based loosely on these, and the big manufacturer's like Fender and Gibson defend their patented shapes and designs vigorously when they feel it necessary.
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Other guitars like the Flying V, Explorer, and some other weird shaped guitars make up the numbers nicely. One company in the eighties really did try to push the boundaries of the shape of the guitar, BC Rich. These were adopted mainly by Heavy Metal bands and the BC Rich Mockingbird was the perfect shape for a metal guitar. Very 'Excalibur'.
Although the need for amplification of the guitar was the catalyst for the creation of the solid body electric guitar, it is by no means the only innovation. And along with it came the ability to control the sound much easier. One of the problems with amplifying an acoustic to high levels was that it was too prone to 'feedback', a high squealing sound that is caused by the sound of the guitar coming through the speakers of PA and then being fed back through the pickup, and out through the speakers again in cycles. If you ever need to annoy a couple of hundred people in a club this is the best way I can think of. The solid body addressed this problem to a great degree, although the problem can still arise on cheap guitars or pickups that have become microphonic. Essentially that is what the pickup is, a microphone. To prove this, the next time you get the opportunity, grab an electric guitar, plug into an amplifier, turn both up, and shout closely into the pickup, you'll hear your magnetic voice coming through the speakers. Cool!
The electric guitar also brought us individually adjustable bridge saddles, to help with string height and intonation, vibrato bridges which allowed the guitarist to alter the pitch of the strings, tone controls to make the sound brighter or warmer as required, and various types of electromagnetic pickups which also change the sound of the guitar. The electric guitar has also spawned a massive accessories and add-ons market with all manner of products available to improve (or ruin) the sound of your guitar such as analog and digital effects (FX) pedals and units, replacement parts for the bits that are already on your guitar, and technologies that allow you to send the guitars electronic signal to a processor to produce any sound imaginable including other traditional instruments like piano, violins, trumpets and saxophones or even a dog barking if you really feel you must.
No matter what the shape or style of the electric guitar, they are still fundamentally the same instrument as the acoustic guitar, they have the same notes on the neck, they are tuned the same, and therefore if you learn to play an electric guitar you can transfer those skills to the acoustic and vice versa, though playing style is generally different between the two.
Oh, and electric guitars do require a little more effort to smash when whacked into a large stack of speakers or battered of a stage floor...
They are an excellent choice for beginners unless you are specifically interested in learning to play classical guitar or folky, finger-picking styles. The necks are easily adjusted to improve the action (the height of the strings from the fretboard) making it easier to press the strings down to the frets, are quite robust, and comfortable to play.
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