An electric guitar consists of a body, neck, and hardware.

	Hardware Tuning Machines Tremolo Block/Bridge Plate Input Jack/Plate Neck Plate and Screws Tremolo Springs Right images from Callahamguitars.com

The electric guitar is a very simple instrument. It is just a nice combination of hardwoods. The body (bottom left) is a solid piece of alder with a quilt maple ply glued to the top. It could be made of any type of wood available, such as plywood. In some cases, I have seen guitars that are made out of plain metal, plastics, and even foam (like in surf boards). The neck is made usually from maple and sometimes has a fret board glued to it to change its tonal characteristics. A truss rod and sometimes graphite rods are installed inside the neck to counteract the tensions from the strings which could warp the guitar neck.

Acoustically, an electric guitar does not have any significant volume. That is how we know the electric guitar as the "electric" guitar! A matter of fact a guitar generates its own electricity! How does it do this? The pickups are a generator of electricity. The strings are an electro-conductive and vibrate around a wire and magnet coil, thus producing an alternating current. This matches the frequency of different pitches and the current is sent to an amplifier, so anyone could "rock out!"

Many people ask me "what is that bar do on that guitar?" It is a tremolo bar, it is used to drop the pitch on the guitar when strumming a chord or playing a harmonic note.

 

image from howstuffworks.com

To tune a guitar, one must apply tension to the string using a tuning machine. This frequency is... (From Noyce Guitars)

figure 1.

image from Noyce Guitars

where

f = fundamental frequency

(first mode of vibration see fig 1)
L = string length between fixed
points (i.e. bridge and nut)
T = string tension
P = string mass per unit length

(Noyce Guitars)

STRING GAUGE FREQUENCY STRING MASS PER UNIT LENGTH TENSION f P T inch/mm cycles/sec (Hz) kg/m kg E or 1st .010/.254 329.63 0.401 x 7.28 B or 2nd .013/.330 246.94 0.708 x 7.22 G or 3rd .017/.432 196.00 1.140 x 7.32 D or 4th .026/.660 146.82 2.333 x 8.41 (.014" core) A or 5th .036/.914 110.00 4.466 x 9.03 (.015" core) E or 6th .046/1.168 82.407 6.790 x 7.71 (.016" core) TOTAL 46.96

(Noyce Guitars)

Nearly 47kg of tension is a lot for a little wooden neck. It is important to have an adjustable truss rod in a guitar neck. Guitar players like the late Stevie Ray Vaughan used really heavy string gauges (.013"-.056") which created so much tension, he had to tune his guitar down a half step (in order of 1st to 6th string: E-flat, B-flat, G-flat, D-Flat, A-Flat, and E-Flat) just to bend the strings much easier.