Electric charge is a fundamental property of matter that determines how objects interact electromagnetically. Positive and negative charges attract each other, while like charges repel. This principle governs everything from static electricity to the behavior of subatomic particles.

Conservation of charge is a key law in physics, stating that the total charge in a closed system remains constant. This concept explains phenomena like static electricity and electric currents, and it's crucial for understanding how charges interact and transfer in various situations.

Electric Charge and Interactions

Electric charge interactions

• Electric charge fundamental property of matter determines electromagnetic interactions
• Two types of electric charge: positive (protons) and negative (electrons)
  • Like charges repel each other (positive repels positive, negative repels negative)
  • Opposite charges attract each other (positive attracts negative, negative attracts positive)
• Protons have a positive charge, electrons have a negative charge
  • Protons and electrons have equal magnitude of charge but opposite signs
• Neutral objects have an equal number of protons and electrons resulting in no net charge
• Charged objects have an imbalance of protons and electrons
  • Positively charged objects have more protons than electrons (net positive charge)
  • Negatively charged objects have more electrons than protons (net negative charge)
• Coulomb's law describes the force between two charged objects
  • $F = k \frac{|q_1||q_2|}{r^2}$, where $F$ is the force, $k$ is Coulomb's constant, $q_1$ and $q_2$ are the charges, and $r$ is the distance between the charges
  • Force directly proportional to product of charges and inversely proportional to square of distance between them
  • Larger charges and smaller distances result in stronger forces

Examples of static electricity

• Rubbing a balloon on hair transfers electrons from hair to balloon
  • Balloon gains negative charge from electrons transferred from hair
• Walking across a carpet and touching a metal doorknob
  • Body accumulates charge from friction with carpet, discharges to doorknob (sparks)
• Removing a sweater or shirt causes static cling
  • Friction between clothing and body can cause garments to stick together
• Combing hair with a plastic comb
  • Comb gains negative charge from electrons transferred from hair (hair stands up)
• Rubbing a glass rod with a silk cloth
  • Glass rod gains positive charge, silk cloth gains negative charge (rod attracts small pieces of paper)

Conservation of charge law

• Law of conservation of charge states net charge in isolated system remains constant
  • Charge cannot be created or destroyed, only transferred or redistributed
• In a closed system, total positive charge must equal total negative charge
• When two objects are rubbed together, they transfer charges but total charge remains the same
  • One object gains the same amount of charge that the other object loses (conservation of charge)
• In any charge interaction or chemical reaction, total charge before and after event remains the same
  • Example: In a battery, chemical reactions transfer charges but total charge is conserved
• Law of conservation of charge is a fundamental principle in physics and chemistry
  • Helps explain various phenomena (static electricity, electric current, chemical bonding)
  • Charge conservation essential for understanding behavior of charged particles and electromagnetic interactions

Electric Fields and Related Concepts

• Electric field: region around a charged object where electric forces are exerted on other charges
  • Represented by field lines showing direction and strength of electric force
• Electric potential: potential energy per unit charge at a point in an electric field
  • Measured in volts, determines the work needed to move a charge in the field
• Polarization: alignment of electric dipoles in a material due to an external electric field
  • Occurs in dielectrics, materials that can be polarized but don't conduct electricity well
• Insulators: materials that resist the flow of electric charge (e.g., rubber, glass)
  • Play important role in controlling and isolating electric charges in various applications