Electric Charge

• All objects in our surroundings hold electric charge in abundance, even our own bodies.
• Electric charge is an intrinsic property of the tiny particles that make up all substances.
• Two opposite types of charges — positive (+) and negative (−) — are always present in equal numbers, keeping objects neutral.
• If these charges are unbalanced, the object is said to be "charged."

The basic property of matter due to which it experiences electric force and shows attraction or repulsion, is called electric charge.

OR

The fundamental property of subatomic particles that gives rise to the phenomenon of experiencing force in the presence of electric and magnetic fields is called electric charge.

• Positive charge: Deficiency of electrons
• Negative charge: Excess of electrons
• SI unit: Coulomb (C)
• Dimension: [M⁰L⁰T¹A¹]

An electric charge which can be considered to exist at a single point is called a point charge.

A unit positive charge used to test the strength of electric fields is called a test charge.

• When a glass rod rubbed with silk is suspended, and another similarly charged glass rod is brought near, the two rods push each other away — this is repulsion.
• When a plastic rod rubbed with wool is brought near the suspended glass rod, they pull towards each other — this is attraction.
• Like charges repel; unlike charges attract.
• Benjamin Franklin named the two types: positive charge (+) and negative charge (−).

• Charge is the basic property of matter that causes objects to attract or repel each other.
• It is carried by subatomic particles — protons carry a positive charge, and electrons carry a negative charge.
• Charges can neither be created nor destroyed.
• Unlike charges attract each other; like charges repel each other.
• Electric charge is measured in coulombs (C).

• The smallest amount of charge that can exist freely is called the elementary charge (e).
• Its value is 1.602 × 10⁻¹⁹ C — this is the charge on each proton and electron.
• Protons carry positive elementary charge (+e), and electrons carry negative elementary charge (−e).
• Since protons and electrons are equal in number, an atom is electrically neutral.

• Every atom has a nucleus with positively charged protons and neutral neutrons, surrounded by negatively charged electrons.
• If an electron is removed from an atom, it becomes a positive ion.
• If an electron is added to an atom, it becomes a negative ion.
• When a plastic comb is rubbed on dry hair, electrons transfer from hair to the comb — hair becomes positive, the comb becomes negative.

• The unit of charge is coulomb (C); the charge of an electron is e = 1.6 × 10⁻¹⁹ C.
• Any charge q must be an integer multiple of e: q = ne, where nn is a whole number.
• One coulomb contains 6.25 × 10¹⁸ electrons.
• Practical sub-units: 1 µC = 10⁻⁶ C, 1 nC = 10⁻⁹ C, 1 pC = 10⁻¹² C.

• When two non-conducting bodies are rubbed, electrons transfer — the body gaining electrons becomes negatively charged, the body losing electrons becomes positively charged.
• The SI unit of charge is coulomb (C); smaller units are milli-coulomb (mC = 10⁻³ C), micro-coulomb (µC = 10⁻⁶ C), nano-coulomb (nC = 10⁻⁹ C).
• Charge on a body is always q = ±ne, an integer multiple of the electron charge.
• In an insulator, charge stays static at the point of excess or deficit of electrons — it does not flow.
• In a conductor, free electrons can move and flow throughout the entire volume.

• When an uncharged conductor is brought near a charged body (without contact), the nearer side develops opposite charge and the far side develops similar charge — this is called induction.
• In induction, no charge is transferred between the charged body and the conductor.
• When the charged body is removed, the charges in the conductor redistribute freely again.

• Around 600 BC, Thales of Miletus (Greece) observed that rubbed amber attracts light objects — the word "electricity" comes from the Greek word electron, meaning amber.
• In 1600, Gilbert discovered that many materials (glass, ebonite, sulphur) can be electrified by rubbing.
• Static electricity causes everyday phenomena — sparks when removing synthetic clothes, lightning during thunderstorms, and shocks from metal surfaces.
• Electrostatics is the study of forces, fields, and potentials arising from static (non-moving) charges.