In principle, an electric violin is nothing more than a violin with an output that allows for amplification.

An acoustic violin needs a hollow body in which sounds resonate and build up. In most electric violins, the vibrations of the strings are directly picked up by some kind of transducer. Electric violins are typically used in high volume situations, in which an amplified acoustic instrument quickly leads to feed-back. Most electric violins have a solid body in which the resonances that potentially lead to feed-back are avoided. The solid body gives luthiers a great opportunity to design original shapes. The shape has a practical importance and determines the overall weight of the instrument, but it is mainly a matter of taste. Shapes vary from rather traditional, over rock-like to avant-garde minimalistic.

The sound of an electric violin is extremely dependent on the transducer and its positioning, the amplification, effects and speaker. Electric violins need similar equipment as electric guitars, and most violinists look into guitar-shops for stuff like amplifiers and effects. However, an elecric violin is a bit more demanding: the requirements are more specific if you want to obtain an optimal sound.

If you're a classical violin player but want to go electric, the shapes and designs of the electric violins might take you by surprise. There are, of course, classical looking electric violins. You can also get started with a pickup on your acoustic violin, in combination with a preamp. This can get very tricky as it is harder to get a clean and strong electrified sound from a regular violin than it is with an electric one. Going electric with your acoustic violin easily results in feedback. A pick-up on an acoustic instrument will usually amplify every little sound of the instrument, including movements of the fingers, knocks in the instrument's body, etc.

You should really consider the alternatives... Electric violins are more durable, their sound is much clearer, they sometimes have built-in equalizers, reduced feedback and they definitely provide better, stronger sounds. And of course, electric violins are most suited for live performances.