Ph-204 Chap 21
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The electric potential V is:
created by charges and exists at every point surrounding those charges.
When a charge q is brought near these charges:
- it acquires an electric potential energy
- Uelec = qV
- at a point where the other charges have created an electric potential V.
Energy is conserved for a charged particle in an electric potential:
- Kf + qVf = Ki + qVi
- ΔK = -qΔV
Potential differences ΔV are created by a separation of charge. Two important sources of potential difference are:
- 1.A battery, which uses chemical means to separate charge and produce a potential difference.
- 2.The opposite charges on the plates of a capacitor, which create a potential difference between the plates.
The electrical potential of a point charge q is:
For a conductor in electrostatic equilibrium:
- 1.Any excess charge is on the surface.
- 2.The electric field inside is zero.
- 3.The exterior electric field is perpendicular to the surface.
- 4.The field strength is largest at sharp corners.
- 5.The entire conductor is at the same potential and so the surface is an equipotential.
The potential difference ΔVC between two conductors charged to ±Q is proportional to the charge:
- ΔVC = Q/C where C is the capacitance of the two conductors.
The permittivity constant or εο:
A parallel-plate capacitor with plates of area A and separation d has a capacitance:
C = κεοA/d
When a dielectric is inserted between the plates of a capacitor, it's capacitance is:
Increased by a factor κ, the dielectric constant of the material.
1.The energy stored in a capacitor is:
2.This energy is stored in the electric field, which has energy density:
- 1.UC= ½C(ΔVC)2 2.UE=½κεοE2
For a capacitor charged to ΔVC the potential at distance x from the negative plate is:
- The electric field inside is:
1V = 1J/C
1 electron volt = 1eV = 1.60x10-19 J is the kinetic energy gained by an electron upon accelerating through a potential difference of 1V.
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