The electric guitar, if you really think about it, is less a reaction against the acoustic guitar and more an extension of it.
Where the acoustic relies on the interaction between itself and its player's hands, the electric puts itself at the mercy of its player's ears. Given the daunting task of supporting a band lineup while simultaneously standing out against it, the electric guitar player is forced to rely on his or her sound rather than his or her music.
And just how does one pull this off? By the addition of external effects to the guitar and amp combination. Most guitar players at least know of wah pedals, flangers, chorus pedals and the like, but very few know much about them, a line of thinking very famously derided by Boston guitarist and studio wizard Tom Scholz in the liner notes to his band's debut album: "People have already fallen prey to that, in my opinion," he wrote, "with items that they just go out and buy to get a certain sound without really understanding where that sound comes from and how to apply it."
Scholz never really elaborated upon his ideas of understanding sound application, but in the eighty-something years of full-volume rock's history a few sound extensions have achieved the status of standard issue and become worth exploring beyond the purely sonic level.
Effect: Chorus
What it Does: As the name suggests, the chorus effect creates a veritable glee club of guitars by repeating the input signal at an extremely close interval. Unlike the digital delay, which usually repeats by some number of milliseconds (1/1,000 seconds), chorus works at microsecond (1/1,000,000 seconds) intervals too close together for the human ear to differentiate as being sequential sounds.
Practical Uses: Besides hard rocking with a distorted tone, chorus added to a clean tone creates the standard lead guitar sound found in modern country pop.
One Really Famous Example: Quite common in heavy metal guitar, chorus-soaked electric is the signature sound of every gunslinger ever employed by Ozzy Osbourne.
Effect: Flange
What it Does: Commonly described as the "airplane whoosh" sound, flange creates a copy of the input signal and sends that copy alongside the original through the outbound signal. The copy will have certain audio properties continually adjusted, primarily the volume of the delayed signal relative to the non-delayed signal. The constant tweaking of the sound results in the altering of the additional guitar track during playing, and the changing delay times are what create the simulated Doppler effect.
Practical Uses: Big guitar lines in a live setting where overdubs are simply not an option.
One Really Famous Example: The "big guitar" parts on Nirvana's Nevermind, most notably the chorus of "Come As You Are."
Effect: Tremolo
What it Does: Tremolo changes the volume of the input signal on the fly, but at a constant interval. Unlike flange, which creates an additional track against the main signal, tremolo adjusts the primary signal itself, causing the sound to drift in and out of audibility. Tremolo comes from either a stompbox, effects board, rack unit or other piece of outboard equipment; many guitars come equipped with a so-called "tremolo bar," but this in fact works to alter pitch, not volume, thus making it cause the tremolo only in name (the true effect in that cause would be vibrato).
Practical Uses: Commonly used but more commonly misused, tremolo most frequently lends itself to a tone best described as "spooky cool."
One Really Famous Example:"How Soon Is Now?" by The Smiths
Effect: Digital Delay
What it Does: Simple yet highly elaborate at the same time, digital delay adds a very precise level of echo to a guitar sound at both a volume and a specified time interval following the initial striking of a note.
Practical Uses: For lead guitar, the digital delay's usefulness is rivaled only by the wah pedal. By adding more notes (even the same notes) into the same musical space, one guitar can suddenly become many guitars. In rhythm settings, the total opposite application becomes infinitely helpful when a lone guitar can suddenly fill the space of numerous. Likewise, using very faint echo settings and longer delay times, digital delay can be used to create that "spacy" sound.
One Really Famous Example: The verses of "I Ran (So Far Away)" by Flock of Seagulls
Bonus Really Famous Example: Pretty much anything by U2
Effect: Wah Pedal
What it Does: The wah pedal (or "wah-wah" pedal, depending on who you ask) cuts out some range of bass frequency while simultaneously boosting some range of treble frequency, and vice versa. For example, with the pedal towards the floor, the low end is almost entirely removed from the input signal while the high end is entirely accented, creating an extremely treble-heavy, almost nasally tone. Conversely, with the pedal all the open, the treble is cut and the bass and mids are boosted, making the guitar sound as though it were underwater.
Practical Uses: In soloing, the fluctuation of the pedal can help create guitar lines more closely mimicking human patterns of speech (not to be confused with the talkbox, which is something else entirely).
One Really Famous Example: Legend has it the original Dunlop wah pedal was dubbed the "Crybaby" in tribute to the sounds Jimi Hendrix was exploring with the pedal in his leads and his riffs; one listen to "Voodoo Chile" and it's hard to argue.
Ironically, the natural tendency for most guitarists is to start with these common examples, master the effect, then instantly revolt against this chosen addition to their musical arsenal. So begins the dreaded G.A.S. (gear acquisition syndrome), but any instrumentalist can take heart: the only way to solve a new problem is to chase a new solution, meaning the quest for sonic expansion will have ended only as it has also just begun. Maybe Scholz was more right than he realized.