Quote:
Originally Posted by tesia   I'm lost in physics. horribly lost. We're studying electric potential and work. totally lost. the notes she gave us do not include anything about distance, yet our worksheets involves distance multiple times. so i'm just lost. i will post one of my quesitons, and i'd love some explanation...  Two parallel conducting plates are connected
to a constant voltage source. The magnitude
of the electric field between the plates is
2107 N /C. If the voltage is quadrupled and
the distance between the plates is reduced
to 1/8 the original distance, what is the
magnitude of the new electric field?
Answer in units of N/C.
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You have to assume that the E field is uniform throughout the region where the plates are (because... figure it out yourself. I give you a tip: what is the E field of an infinite charged plate?). With this assumption, E=V/d. You can then solve easily the problem.
Why does E=V/d? It follows from the definition of the potential function, namely E=-grad(V). Thus V(r)=-int _(infinity)^r E dr where E and dr are vectors. It turns out that if E is parallel to dr, such as in this case, and that E is constant, the simplification done holds.