Electric Potential Energy and Charge in Electric Fields, Slides of Physics

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Electric Energy

Electrical Potential Energy

^

Potential energy is the negative of the work done byconservative forces.•^

Potential energy

 U

=^ 

Wcon

^

Electrical work is done by the Coulomb force.•^

Electrical potential energy

Potential Difference

^

The potential energy isexpressed as a difference ofthe energy of two states. ^

The electric potential can beexpressed with respect to atest charge.

qEd^ q U^

q

d F

E

 U

U q V^

Point Potential

^

Coulomb’s law ismathematically similar togravitational force.•^

Define potential energysimilarly• Point charge

Q

-^ Test charge

q

^

Apply the definition of theelectric potential. ^

Like gravity zero is at infinity.

^   

i f^

r r kqQ U^

^   

i f^

r r kQ V^

kQ^ r V^

Arbitrary Zero

^

The zero of potential energy isarbitrary. ^

U^ can be defined, but

 U

is

what really matters.•^

Compare energy to work ^

We can measure the change inelectric potential

V.

-^ No experiment reveals thespecific value

E

V^ = 0

q

Vf

Charge Energy

^

The electric force isconservative.•^

Energy is conserved• Independent of the experiment ^

Suppose that charge were notconserved.•^

An experiment would be ableto cause some charge tovanish• Loss of specific amount ofpotential energy• Inconsistent with energyconservation

E

V^ = 0

q

Vf