Electrostatics: Electric Charge

Electric Charge

  • Definition: Electric charge (Q or q) is a physical property of matter that allows an object to exert an electric force on another object without touching it.
  • Unit of Measurement: Measured in coulombs (C).

Key Concepts

  • Electric Charge
    • Exists in two types: positive (+) and negative (-) charges.
    • Atoms are typically neutral, meaning they contain equal amounts of positive (protons) and negative (electrons) charges.
  • Static Electricity: Accumulation of excess electric charges (positive or negative) on a body, which remain at rest.
  • Electrostatics: Study of static electricity (stationary electric charges).
    • Example: Rubbing a balloon on hair creates static electricity, leading to an electrostatic force greater than gravity.

Interactions of Electric Charges

  • Like Charges: Repel each other (e.g., positive repels positive).
  • Unlike Charges: Attract each other (e.g., positive attracts negative).
  • Neutral Objects: Neutral objects are attracted to charged objects.

Conductors and Insulators

  • Conductors: Materials allowing charges to move easily (e.g., metals like copper, aluminum).
  • Insulators: Materials where charges do not move easily (e.g., glass, rubber, dry wood).
  • Behavior of Conductors: Charge spreads out evenly on a conductor; insulators hold charges in place.

Charge Transfer and Calculation

  • Process: Charges are transferred (typically electrons) through processes like friction (e.g., rubbing wool on rubber).
  • Net Charge Calculation: The net charge of an object can be calculated using the formula: Q = n imes e
    • Where Q = net charge (in coulombs)
    • n = number of charges
    • e = elementary charge of a single electron (approximately 1.6 imes 10^{-19} C).
  • If an object gains electrons: Q = -n imes e (negatively charged).
  • If an object loses electrons: Q = n imes e (positively charged).

Observable Phenomena

  • Example of Charge Transfer: When rubber is rubbed with wool, electrons are transferred from wool (positively charged) to rubber (negatively charged).
  • Excess Electrons: An electroscope with a charge of -1.44 imes 10^{-16} C can be analyzed to find the number of excess electrons using the aforementioned formula.

Summary of Key Points

  • Electric charge is a cornerstone of electrostatics, explaining various phenomena like static cling and lightning.
  • The conservation of charge states that charges are neither created nor destroyed, only transferred.
  • Understanding charge and its properties is foundational to modern technology, such as batteries and electronics.