Electric-Charges

Electric Charge Overview

  • Electric charge is a fundamental property of matter, affecting how objects interact with each other through electric forces.

Atoms & Electricity

  • All matter is composed of atoms, consisting of

    • Electrons (e-)

    • Protons (p+)

    • Neutrons (n)

  • Electrons and protons are electrically charged, while neutrons are neutral and do not participate in electric interactions.

  • Objects with equal numbers of electrons and protons are termed neutral.

  • An imbalance in electrons and protons results in an electrically charged object.

Types of Electric Charge

  • An object with more electrons than protons is negatively charged.

  • An object with more protons than electrons is positively charged.

  • The imbalance between p+ and e- is usually very small (e.g., 1 in 10 trillion).

Conservation of Electric Charge

  • Charge is conserved: it cannot be created or destroyed but can be transferred.

  • Like charges repel each other while opposite charges attract.

Units for Electric Charge

  • The symbol for electric charge is "q."

  • Elementary charge unit (e):

    • For a proton: +1e

    • For an electron: -1e

  • SI unit for charge is the Coulomb (C).

  • One Coulomb is defined as the charge of electrons passing through a current of 1 Amp each second: C = A.s.

  • Conversion: 1 e = 1.60 x 10^-19 C (noted from Robert A. Millikan).

Polarization

  • Neutral objects can become electrically active through polarization when brought near a charged object.

    • Electrons and protons move in opposite directions when a charge is near.

  • The edges of the object acquire opposite charges, leading to attraction toward the charged object.

  • The force is stronger on the side closer to the charge due to proximity.

Permanent Polarization

  • Some molecules, such as H2O, have permanent dipoles (+ and - ends).

  • When charged, these molecules rotate to align opposite charges close together, leading to attraction.

Charging Methods

  • Charging by Friction

  • Occurs when two different materials rub against each other, transferring electrons.

  • The material with higher electron affinity becomes negative, while the other becomes positive (e.g., balloon rubbed on hair).

  • Charging by Conduction

  • Involves contact between a neutral object and a charged one, allowing electrons to transfer.

  • If the charged object is negatively charged, electrons can move from the charged object to the neutral one.

  • Protons in solids are stationary; charge distribution is on the surface of conductive materials after contact.

  • Charging by Induction

  • Involves a charged object influencing another without direct contact, causing charge movement.

  • If object B is connected to a distant object, like Earth, charge separation occurs as a result of the induced electric field.