Notes on Chapter 24

Notes on Chapter 24 - Chapter 24 Electric Potential 24-1...

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17 June 2010 1 Chapter 24 – Electric Potential A conservative force has potential energy associated with it Hence we can apply the principle of conservation of energy to closed systems involving the force The electric force is a conservative force ; its associated potential energy is the electric potential energy 24-1 What is Physics?

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17 June 2010 2 Work- Energy Theorem cos dW F dl F dl φ = = If is conservative , then the work done can by can be expressed In terms of a potential energy, U such that: F F () f i if f i W F dl U U U = ⋅ = − − = −∆ and 0 If 0, then if i f U W UU ∆< >> and 0 If 0, then i f U W ∆> << 24-2 22 2 11 1 II . cos PP P P W F dl F dl F dl = = ∫∫ Electric Potential Energy
17 June 2010 3 If the work is done by conservative force only then if f i i f W K K K U UU = = = −∆ = ii f f KU K U += + (Conservation of mechanical energy) Since electric forces are c onservative , there is an electric potential energy U associated with a system of charged particles. A change in U is then given by: () i f f i W U U U = = = Or, fi U W ∆= = By convention and , 0, i f U U UW = = = −

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17 June 2010 4 Electric Potential Energy of TWO Point Charges r 2 At , r F r qQ k r = 2 1 11 B A B B A A r r r r r r AB r UU W F dr dr kqQ kqQ kqQ r rr r    = − = = = −= Note: as expected for a conservative force, the work done depends only on the end points. F r
17 June 2010 5 Electric Potential The electric potential V ( also simply called the potential ) is defined as the electric potential energy per unit charge U V q = A scalar quantity The potential difference ∆V between two points i and f in an electric field is defined as the difference in potential energy per unit charge between the two points if f i fi WU U U V VV q q qq

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Notes on Chapter 24 - Chapter 24 Electric Potential 24-1...

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