Electrostatics

• How to Interpret a Graph of Electric Potential
  Learn how to read electric-potential graphs, calculate electric field from their slope, and interpret straight, curved, flat, and discontinuous regions.
• Why Does Gravity Hold the Planets in Orbit if Electric Forces Are Stronger?
  Electric forces between particles can dwarf gravity, but stars and planets are nearly neutral; their mass adds up, so gravity governs their orbits.
• How Are Coulomb’s Law and Electric Field Intensity Related?
  Coulomb’s law gives the force between charges; electric field intensity is the force per unit positive test charge at a point.
• Can the Inner Surface Charge Density Be Negative?
  Yes. A positive charge inside a spherical conducting cavity induces negative charge on the inner wall; mixed-sign interior charges can make the density change sign.
• How to Reveal Electric Field Lines with Grass Seeds in Mineral Oil
  Use polarized grass seeds in insulating mineral oil to trace electric-field direction; learn the setup, what the pattern means, and how to work safely.