Electrostatics

Electrostatics

1. Point charge

   • Field lines
     • Point away from +charge, towards -charge
   • Positive and negative
     • Like-charges repel
     • Opposite charges attract
   • Fundamental charge = +/- 1.6 x 10^-19 C

2. Dipoles

3. Electric field

   • Electric Flux
     • Amount of electric field passing through an effective surface
       • Max = surface is perpendicular to field
     • Flux = EAcos0
     • Independent of surface shape/radius, dependent on amount of charge
   • Velocity and acceleration
   • Between two parallel conducting plates = uniform
   • Inside conductor= 0
     • Perpendicular to surface

4. Potential Energy

   • Neutral particle = (change)U = 0, as F=Eq=0
   • F = Eq
   • (change)U = -W
     • Work done by Coulomb's force comes from electric potential energy
   • Electric Potential
     • V = U(electric) / q
     • V = E d
     • Equipotential lines
       • Points at the same electric potential are linked via equipotentials (contour lines)
         • Electric field is stronger where equipotentials are closer
         • Perpendicular to the field
       • Pointy conductors
         • Strong electric field and charge density at the tip = due to close spacing of equipotentials

5. Conductor

   • Charging by contact
   • Polarization
   • Charging by Induction
     • Charged rod separates charge on conductors (not touching)
       • Conductors are polarized due to charging rod
   • Charge is able to redistribute itself throughout a conductor
     • All charge is on the surface

6. Insulator

   • Charge is unable to move freely within an insulator

7. Coulomb's Law

   • Electric Force
     • F = k(q1 x q2) / r^2
       • Electrostatic constant, k

8. Gauss' Law

   • Enclosed charge
   • Gaussian surface = closed surface around a charge
   • Flux = (integral) E. dA = q(enclosed) / e