Physics 121: Electricity & Magnetism – Lecture 2 Carsten Denker NJIT Physics Department Center for Solar–Terrestrial Research

January 24, 2007Center for Solar-Terrestrial Research Introduction  Charges and Forces  Electric Field  Electric Field Lines  Electric Field Due to a Point Charge  Electric Field Due to an Electric Dipole  Electric Field Due to a Line Charge  Point Charge in an Electric Field  Dipole in an Electric Field

January 24, 2007Center for Solar-Terrestrial Research Electric Field  Uranium nucleus: 3  N/C  Electric breakdown in air: 3  10 6 N/C  Photocopier drum: 10 5 N/C  Charged comb: 10 3 N/C  Copper wire: 10  2 N/C  Scalar fields: temperature, pressure, …  Vector fields: electric field, flow field, … Electric field

January 24, 2007Center for Solar-Terrestrial Research Electric Field Lines Electric field lines extend away from positive charge (where they originate) and toward negative charge (where they terminate). Electric Dipole

January 24, 2007Center for Solar-Terrestrial Research Electric Field Due to a Point Charge Point charge Superposition principle

January 24, 2007Center for Solar-Terrestrial Research Electric Field Due to an Electric Dipole and a Line Charge  Point charge q [C]  Line charge density [C m  1 ]  Surface charge density  [C m  2 ]  Volume charge density  [C m  3 ]

January 24, 2007Center for Solar-Terrestrial Research Point Charge in an Electrical Field The electrostatic force acting on a charged particle located in an external electric field has the direction of if the charge q of the particle is positive and has the opposite direction if q is negative. Ink–jet printer Millikan experiment

January 24, 2007Center for Solar-Terrestrial Research Dipole in an Electric Field Torque Potential energy