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

2. 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

3. January 24, 2007Center for Solar-Terrestrial Research Electric Field  Uranium nucleus: 3  10 21 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

4. 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

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

6. 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 ]

7. 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

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