AP PHYSICS 2
SUMMARY CHAPTER 15 – THE ELECTRIC FIELD
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E field The E field is a force-like quantity characterizing the electric field at a specific location. A source charge
creates an electric field that exerts a force on a test charge placed in that field at that location. The E field at a the
chosen location is equal to the electric force exerted by a source charge on a positively charged test object divided
by the test object’s charge
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Superposition principle The E field at a location is the vector sum of the contributions on n source charges to the E
field at that location.
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V field (electric potential) is an energy-like quantity characterizing the electric field at a point. The V field (electric
potential) at a position of interest is equal to the electric potential energy Uq of a small positively charged test
charge QT and the source charge divided by the rest object’s charge. Include the signs of charges when calculating
Uq.
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Superposition principle for V field The V field at a specific location is the algebraic sum of the contributions on n
source charges to the V field at that location.
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Relationship of E field and V field The greater the magnitude of the E field at a particular location, the faster the V
field changes with position near that location. The E field points from higher V field values to lower V field values.
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Representing the E field and the V field E field lines and equipotential surfaces represent the field. E field lines are
perpendicular to equipotential surfaces.
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Dielectric constant K A dielectric material partially cancels the E field within it produced by the environment. This
reduces the magnitude of the force exerted by charged objects on each other within the material.
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Capacitors A device that (when charged) stores electric potential energy. It has two conducting surfaces separated
by a nonconducting material. To charge a capacitor, one connects its plates to the points at different electric
potential (like the terminals of a battery). The charge separation stores electric potential energy in the capacitor.