L1

Objectives

  • Explain electrical interactions using the law of conservation of charge.

  • Explain electrical interactions in terms of attraction and repulsion of charges.

  • Compare conduction and induction.

  • Explain charge distribution on conductors and insulators.

Electrical Interaction

  • Electricity is essential for modern life (music, movies, video games).

  • Early observations by Thales: Rubbing amber attracts small objects, termed "electricity" (from "elektron").

  • Ancient Greeks identified two charge types: like charges repel, unlike charges attract.

Key Historical Figures

  • William Gilbert:

    • Electrical effects require recent rubbing; no rubbing needed for magnetism.

    • Electrified objects attract various materials; magnets attract few.

    • Electrified objects centralize attraction; magnets have two poles.

  • Benjamin Franklin:

    • Connected lightning to electricity via kite experiment.

    • Identified positive and negative charges.

Electrostatics

  • Study of electric charges at rest; examines forces and behaviors of charges.

  • Atoms consist of protons (positive) and electrons (negative), normally electrically neutral.

Electrical Conductivity

  • Conductivity depends on electron binding:

    • Insulators: Electrons tightly bound, unable to move.

    • Conductors: Electrons free to move in outer regions.

Methods of Charging Objects

  • Charging via electron transfer occurs:

    1. Friction

    2. Conduction

    3. Induction

Law of Conservation of Charge

  • Charges in an isolated system are conserved and merely rearranged.

  • Charge unit: coulomb (C) = charge of $6.25 \times 10^{18}$ electrons/protons.

Charging Methods

  • Friction: Electrons are transferred through rubbing, depositing from one object to another.

  • Conduction: Charging by direct electron transfer through contact.

  • Induction: Charges in a neutral object shift due to an external charged object's presence.

Applications

  • Use electrostatic series to predict charging behavior (e.g., ebonite vs. fur).

  • Charge a glass sphere positively by:

    • Friction: Rub with a material that holds electrons tightly.

    • Conduction: Touch a positively charged object.

    • Induction: Bring a positively charged object near, then ground the sphere before removing the charger.

  • Effects of a negatively charged rod near a neutral object:

    • Before touch: Attraction occurs as charge affects distribution.

    • After touch: Charge transfer results in both objects having a similar charge.