Physics 4B: Electricity and Magnetism

Instructor Introduction

• Instructor: Frank Cascarano
• Course Focus: Applications of electricity and magnetism in everyday life (e.g., photocopy machines, magnetic stripes on credit cards, speakers).

Key Topics in Electricity and Magnetism

Electrostatics

• Electric Charge and Atoms

  • Electric charge originates from the atom.
  • Atom components: Nucleus (protons and neutrons) and electron cloud.
  • Protons: Positive charge, located in the nucleus.
  • Electrons: Negative charge, form a cloud around the atom.
  • Neutrons: Neutral, no electric charge.

• Electric Neutrality and Charging

  • Objects are usually electrically neutral (equal protons and electrons).
  • Charging involves adding or removing electrons.
  • Protons define an atom's identity (fixed), electrons can be transferred.
  • Charging by friction: Transfer of electrons when materials rub together.
  • Triboelectric Series: Determines which materials gain or lose electrons.

Interaction of Charges

• Like Charges

  • Like charges repel (e.g., two positive or two negative charges).

• Opposite Charges

  • Opposite charges attract.
  • Demonstration: Balloon rubbed against hair becomes attracted to insulators and conductors.

• Charged vs. Neutral Objects

  • Charged objects can attract neutral objects through induced polarization.
  • Demonstration: Balloon attracts to an insulating wall and conductive pie plate.
  • Neutral objects show polarization:
    • Insulators: Electron cloud shifts creating a polarized atom.
    • Conductors: Electrons move freely, creating charge separation.

Demonstrations and Predictions

• Balloon and PVC Pipe

  • Both objects charged negatively repel each other.

• Balloon and Wall/Pie Plate

  • Balloon attracts both insulator (wall) and conductor (pie plate).

• Charged PVC Rod and Aluminum Can

  • PVC rod attracts a neutral aluminum can by inducing charge separation.

• Paper and PVC Rod

  • Neutral paper initially attracted, becomes charged upon contact, then repels.

Summary

• Understanding charge interaction is crucial in predicting electrical behavior.
• Conductors and insulators behave differently under influence of electric fields.
• Observations: Both attractive and repulsive forces are pivotal in charge interactions.
• Practical applications extend from fundamental charge interactions to complex systems like electronics.