More info on exp ?

I have questions but Not real sure If anyone has an answer. You get exp fro being nearby to minions when they die. Do you get less if there are more champ nearby ? Is there a way to tell if you are too far away like most of the spells show ? The other thing is if your in the jungle does killing the the jungle creatures work the same ? is somebody else come do they share the exp for being in range ??? or are is the exp only last strike on them ????