# reviewnotes - Review of Chapter 25 When a positive test...

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Review of Chapter 25 When a positive test charge q 0 is moved between points A and B in an electric field E , the change in the potential energy of the charge-field system is (25.1) The electric potential V = U / q 0 is a scalar quantity and has the units of J/C, where 1 J/C = 1 V.

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Review of Chapter 25 The potential difference between points A and B in an electric field E is defined as (25.3)
Review of Chapter 25 The potential difference between two points A and B in a uniform electric field E , where s is a vector that points from A to B and is parallel to E is (25.6) where d = | s |. An equipotential surface is one on which all points are at the same electric potential. Equipotential surfaces are perpendicular to electric field lines.

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Review of Chapter 25 If we define V = 0 at r A = infinity, the electric potential due to a point charge at any distance r from the charge is (25.11) We can obtain the electric potential associated with a group of point charges by summing the potentials due to the individual charges. The electric potential due to a continuous charge distribution is (25.20)
Review of Chapter 25 If we know the electric potential as a function of coordinates x , y , z , we can obtain the components of the electric field by taking the negative derivative of the electric potential with respect to the coordinates. For example, the x component of the electric field is (25.16)

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Review of Chapter 25
Capacitors s Capacitors are devices that store electric charge s Examples of where capacitors are used include : s radio receivers s filters in power supplies s energy-storing devices in electronic flashes

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Definition of Capacitance s The capacitance , C , of a capacitor is defined as the ratio of the magnitude of the charge on either conductor to the potential difference between the conductors s The SI unit of capacitance is the farad (F) Q C V = Δ
Makeup of a Capacitor s A capacitor consists of two conductors s These conductors are called plates s When the conductor is charged, the plates carry charges of equal magnitude and opposite directions s A potential difference exists between the plates due to the charge

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More About Capacitance s Capacitance will always be a positive quantity s The capacitance of a given capacitor is constant s The capacitance is a measure of the capacitor’s ability to store charge s The farad is a large unit, typically you will see microfarads ( μ F) and picofarads (pF)
Parallel Plate Capacitor s Each plate is connected to a terminal of the battery s If the capacitor is initially uncharged, the battery establishes an electric field in the connecting wires

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Parallel Plate Capacitor
Parallel Plate Capacitor, cont s This field applies a force on electrons in the wire just outside of the plates s The force causes the electrons to move onto the negative plate s This continues until equilibrium is achieved s The plate, the wire and the terminal are all at the same potential s At this point, there is no field present in the wire and the movement of the electrons ceases

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## This note was uploaded on 11/01/2009 for the course PHY phy2049 taught by Professor Wilfredngwa during the Fall '09 term at University of Central Florida.

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reviewnotes - Review of Chapter 25 When a positive test...

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