Electric charge is a fundamental property of matter that causes forces between particles. Positive and negative charges exist, with like charges repelling and unlike charges attracting. Understanding charge is key to grasping electrostatic interactions.

Charge can be transferred between objects through friction or induction. Materials are classified as conductors or insulators based on how easily charges move through them. These concepts form the foundation for exploring electrostatic phenomena and Coulomb's Law.

Charge and its Types

Electric Charge Fundamentals

• Electric charge is a fundamental property of matter that causes it to experience a force when placed in an electromagnetic field
• Measured in coulombs (C), where 1 C is the charge of approximately $6.24 \times 10^{18}$ electrons or protons
• Two types of electric charges exist: positive and negative
• Like charges repel each other, while unlike charges attract each other

Subatomic Particles and Charge

• Protons are positively charged subatomic particles found in the nucleus of an atom
  • Have a charge of $+1.602 \times 10^{-19}$ C
  • Number of protons in an atom determines the element's atomic number
• Electrons are negatively charged subatomic particles that orbit the nucleus of an atom
  • Have a charge of $-1.602 \times 10^{-19}$ C
  • In a neutral atom, the number of electrons equals the number of protons
  • Electrons can be transferred between objects, resulting in a net charge on the objects (plastic rod rubbed with fur)

Charge Transfer

Conductors and Insulators

• Conductors are materials that allow electric charges to flow freely through them
  • Examples include metals (copper, aluminum, silver), graphite, and salt water
  • Electrons in the outermost shell of conductor atoms are loosely bound and can move easily
• Insulators are materials that do not allow electric charges to flow freely through them
  • Examples include rubber, plastic, glass, and dry air
  • Electrons in insulator atoms are tightly bound to their nuclei and cannot move easily

Methods of Charge Transfer

• Charging by friction occurs when two materials are rubbed together, causing electrons to transfer from one material to the other
  • Example: rubbing a glass rod with silk transfers electrons from the glass to the silk, leaving the glass positively charged and the silk negatively charged
• Charging by induction occurs when a charged object is brought near a neutral conductor, causing the charges in the conductor to redistribute
  • Example: bringing a positively charged rod near a neutral metal sphere causes the electrons in the sphere to be attracted to the side nearest the rod, leaving the opposite side positively charged
  • The sphere remains neutral overall, but the charge distribution is altered by the presence of the nearby charged object