Lecture Notes: Charging by Conduction and Induction

Introduction to the Electroscope

• Instrument for demonstrating electric charge
• Components:
  • Metal ball (top)
  • Vertical metal rod (with hook)
  • Two thin aluminum foils (hanging from hook)
• Insulated from surroundings (rubber stopper and glass flask)

Charging via Conduction

1. Initial Setup

   • Charge a rubber balloon by rubbing it against fur.
   • Balloon becomes negatively charged, fur becomes positively charged (charging by friction).

2. Demonstration Steps

   • Bring charged balloon close to the electroscope → foils move apart.
   • Touch balloon to electroscope → charges transfer, charging the electroscope.
   • Touching the electroscope with a finger acts as a ground, allowing excess electrons to flow into the ground, neutralizing the electroscope.

Key Concepts

• Electrons Movement

  • Electrons move from the balloon to the electroscope when touched.
  • Electroscope ends with a net negative charge (before grounding).

• Conservation of Charge

  • Total electric charge remains constant in an isolated system.

• Ground Concept

  • Ground is a source of charge carriers (infinite relative to objects).
  • Electroscope returns to neutral when extra electrons are transferred to ground.

Summary of Charging by Conduction

• Objects must touch.
• Objects end with the same sign of net charge (both negative).

Charging via Induction

1. Initial Setup

   • Charge a balloon (as before).

2. Demonstration Steps

   • Bring balloon close to electroscope without touching → foils move apart.
   • Touch electroscope with finger (grounding) → some electrons leave to ground due to repulsion, resulting in a net positive charge.
   • Remove balloon, foils repel due to excess protons.

Key Concepts

• Induction Process
  • No direct contact between balloon and electroscope.
  • Electroscope ends with a net positive charge, balloon remains negatively charged.

Summary of Charging by Induction

• Objects never touch.
• Objects end with opposite net charges (balloon: negative, electroscope: positive).

Closing Remarks

• Understanding both conduction and induction is crucial for studying electric charge behavior.