Lecture_09

Lecture_09 - Introduced the concept of electric field E to...

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Unformatted text preview: Introduced the concept of electric field E to deal with forces Introduced electric potential V to deal with work and energy Electric potential: electric potential energy per unit charge Potential Energy Potential energy is associated with pairs of interacting objects A single particle has no electric potential energy Work Work done on a particle is the product of the force exerted on the particle times the displacement through which the force acts: W = F l Units: Joules In Cartesian coordinates: W = F x x + F y y + F z z q 1 q 2 r 12 E 1 + E 2 W int = W ext U el - W int K system + U el = W ext + Q Total energy of the system can be changed ( only ) by external forces. Work done by internal forces: Electric Potential Energy of Two Particles Energy of the system: 1. Energy of particle q 1 2. Energy of particle q 2 3. Interaction energy U el To change the energy of particles we have to perform work. E 1 + E 2 = W ext + W int + Q if ( mc 2 ) = : Energy Principle for a multiparticle system. U el = W int = F int d l i f Example An electron traveling to the right enters capacitor through a small hole at A. Electric field strength is 2x10 3 N/C. What is the change in the electrons potential energy in traveling from A to B? What is its change in kinetic energy? ( AB)= 4mm = (1.6x10-19 C)(2x10 3...
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Lecture_09 - Introduced the concept of electric field E to...

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