Phys 4, Section
1
Jan 25, 2002
Electric Potential Energy
If forces act, then work can be done; if work is done there may be changes in
kinetic energy and potential energy. Note that the electric force is
conservative; only when we treat resistance in circuits will we have to worry
about losses.
W = ∫F•ds
If the force is conservative, the work W can be expressed in terms of
potential energy U :
W_{ab} = ΔU_{ab}
Also, note that for conservative forces, the total mechanical energy K + U is
constant. Note that W is work done by the system, not work done on
the system by external forces.
For charge q_{o} in a uniform field E moving a distance
d in the direction of E:
W = Fd = q_{o}Ed
The change ΔU is q_{o}Ed
since W = ΔU
Electric Potential Energy of Two Point Charges
F = kqq_{o}/r^{2}
Let r_{a} be at infinity and define the potential energy
between charges to be zero for infinite separation. Then for any charge q_{o}
located at distance r from charge q, the electric potential energy
is
Last modified on January 31, 2002
