Yes there is a difference. The wood on the fiddle is going to be a little thinner than the wood in a violin. The Violin is going to be thicker because the strain from the strings.
I have seen, on this site, several answers which make the violin and the fiddle identical instruments. In fact, my teacher, Boris Schwarz, used to call his instrument a fiddle (though he played classical violin). There is a difference, however, between the two. On the violin, the bridge has a typical curve that raises the strings and separates them from one another. Bariolage (moving from string to string and back again rapidly) is possisble because of the nature of this bridge. However, on a fiddle the artist might NOT want this traditional curve to the bridge and ask the maker to REDUCE the curve of the bridge to make bowing and double stopes easier.
The size of a Violin is measured by the size of the body only. A 4/4 ("Full Size") Violin tends to have a body size of around 14 inches. As violin sizes are non-standardized, this size will vary depending on who made the violin, when it was made and where.
It depends on your electric violin. A hollow-body violin with an acoustic pickup (basically, a traditional violin with a microphone built into it) will make sound just like a standard acoustic violin. A solid-body electric violin will make sound without an amp...but unless you're the violin player, you won't hear it.
Spruce or maple.
On your chin in the chin rest.
The head, the neck, and the body.
The fiddle or viol had a much more guitar-shaped body and a different shape of soundhole. They also lacked a soundpost, which dramatically altered the sound.
wood . ( unless electric then it is metal)
Mostly wood.
Type of wood, shape of body (every little difference matters), placement of f holes, action on the strings, and the bow. You'd be surprised how much the bow matters. A violin I had once sounded great with one bow, and average with another.
The main bit is the body, the bit of wood that holds up the strings is the bridge. those are in the middle of the violin, but can you be more specific?
The vibration takes place in the body.