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Homework Statement
I have two problems, both using different equations for electric potential. Confused on when to use which.
First problem:
Two parallel plates connected by a battery whose electric potential is 12V. One plate Has charge density σ^{+} and the other has Charge density σ^{+}. The plates are spaced 3x10^{3}m. We want to find the electric field. The way the problem is solved:
ΔV=U/q
U=qEd
Combining the two above:
ΔV=Ed→E=ΔV/d→E=12V/(3x10^{3}m)=4x10^{3}V
The next problem wants to know the electric potential energy of moving a proton like the attached picture.
It is solved like this:
ΔV=Ed=(8x10^{4}V/m)(0.5m)=4x10^{4}V
Then:
ΔU=qΔV=(1.602x10^{19}C)(4x10^{4}V)=6.4x10^{15}J
My question:
Why I’m the first problem did we say ΔV=Ed
And in the second problem
ΔV=Ed?
Thanks!
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