Physics (university) · Part 07
Electric fields and potential
Charge, Coulomb's law, fields, Gauss's law, potential and capacitors.
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- Electric chargeA property of matter that comes in two kinds, positive and negative. Like charges repel and unlike charges attract. Charge is conserved and comes in units of e = 1.6e-19 C.
- Coulomb's lawThe force between two point charges is F = k q1 q2 / r squared, with k = 8.99e9 N m squared per C squared.
- Electric fieldThe force per unit of positive test charge at a point, E = F/q. For a point charge E = k q / r squared.
- Field linesLines that show the direction of the field. They start on positive charge, end on negative charge, and are closer where the field is stronger.
- Gauss's lawThe total electric flux through a closed surface equals the enclosed charge divided by epsilon zero.
- Conductors in equilibriumIn a conductor at rest the electric field inside is zero and extra charge sits on the surface.
- Electric potentialPotential energy per unit charge, V = U/q. For a point charge V = k q / r. The unit is the volt, one joule per coulomb.
- Potential differenceVoltage between two points. A charge q moved across a voltage V gains energy qV.
- Uniform field between platesBetween two parallel charged plates the field is steady and equals voltage divided by plate gap, E = V/d.
- CapacitanceThe charge stored per volt, C = Q/V, in farads. A capacitor stores energy U = 1/2 C V squared.