Basic Principles of Static Electricity

Introduction

• Everyday examples of static electricity: doorknob shock, balloon hair trick, lightning.
• Static electricity: Imbalance of electric charge seeking equilibrium.

Tape Experiment

• Scenario 1: Two pieces of tape stuck to table, then ripped off and repelled each other.
• Scenario 2: One piece of tape on top of another, ripped off and separated, attracted each other.
• Explanation:
  • Scenario 1: Both tapes stole negative charges from the table – repelled each other.
  • Scenario 2: One tape stole negative charges from the other – opposite charges – attracted each other.

Basic Concepts

• Electric Charge: Objects can be positively, negatively, or neutrally charged.
• Atoms:
  • Composed of protons (positive) and electrons (negative).
  • Electrically neutral atoms have an equal number of protons and electrons.
• Free Electrons: In solids, protons are stationary, but some electrons (valence electrons) can move.
• Conductors and Insulators:
  • Conductors (e.g., copper) allow free electrons to move freely.
  • Insulators (e.g., wood) hold electrons tightly.

Causes of Electron Movement

• Imbalance of Electrical Charge: Different numbers of free electrons in different parts of an object.
• Charging by Friction: Rubbing objects transfers electrons, creating an imbalance (e.g., glass rod and cloth).
• Law of Conservation of Electric Charge: Total charge remains constant; charge is transferred, not created.
• Charging by Contact: Contact between objects allows electron transfer until charge is balanced.
• Charging by Induction: Redistribution of charge within an object without contact, leading to polarization.
• Grounding: Connecting a charged object to a larger neutral conductor (e.g., Earth) allows excess charge to dissipate.

Quantifying Electrostatic Forces

• Coulomb’s Law:
  • Force (") between charged particles: F proportional to the product of charges (q1, q2) divided by distance squared (r²).
  • Includes Coulomb’s Law constant (k = 9 × 10⁹ N m²/C² for air/vacuum).
• Units: Charge measured in Coulombs (C).
• Elementary Charge: Charge of a single electron (e = -1.6 × 10⁻¹⁹ C).
• Examples:
  • Two electrons 1 nanometer apart repel each other with a force of 2.3 × 10⁻¹⁰ Newtons.
  • An electron and proton at the same distance attract with a force of -2.3 × 10⁻¹⁰ Newtons.

Conclusion

• Understanding electrostatic forces: Basics of charge movement and interaction through Coulomb’s Law.
• Preview of next topic: Electric fields and their effects.