Overview
This lecture introduces the concept of electric charge, the structure of the atom, and the basics of electricity including current and conductors, with key definitions and real-life examples.
Atomic Structure
- Matter is made of atoms, which are too small to be seen with the naked eye.
- The Bohr model represents atoms with a nucleus at the center containing neutrons (no charge) and protons (positive charge).
- Electrons (negative charge) orbit the nucleus in defined shells.
- Each shell holds a specific number of electrons: 2 in the first, 8 in the second, 18 in the third, etc.
- The number of electrons in the outermost (valence) shell determines atomic reactivity.
- Atoms are most stable and least reactive when their valence shell is full.
Electric Charge and Ions
- Atoms are normally neutral, having equal numbers of protons and electrons.
- Atoms can gain electrons (becoming negatively charged) or lose electrons (becoming positively charged).
- A charged atom is called an ion.
- Static electricity is caused by transferring electrons, creating temporary charge imbalances.
Conductors and Insulators
- Conductors (e.g. metals) allow free movement of electrons, enabling electric current.
- Insulators (e.g. plastic, glass) hold electrons tightly, limiting current flow.
- Free electrons in conductors facilitate electricity.
Conservation of Electric Charge
- The total electric charge is conserved; charge can move but not be created or destroyed.
- The law of conservation of electric charge states that net electric charge is always constant.
Electric Charge and Current
- Electric charge is denoted by q and measured in coulombs (C).
- The elementary charge (e) is ±1.6 × 10⁻¹⁹ C; protons have +e and electrons -e.
- One coulomb equals 6.24 × 10¹⁸ electrons.
- Electric current is the flow of electric charge, measured in amperes (A).
- Current (I) is defined as one coulomb per second passing through a wire.
Electric Circuits and Current Flow
- In closed circuits, conductors like copper wire let electrons flow from the battery's negative terminal to the positive.
- Components (e.g. light bulbs) in the circuit use the moving electrons to produce effects like light.
Key Terms & Definitions
- Atom — Smallest unit of matter, composed of protons, neutrons, and electrons.
- Electron — Negatively charged particle orbiting the nucleus.
- Proton — Positively charged particle in the nucleus.
- Neutron — Neutral particle in the nucleus.
- Valence Shell — Outermost electron shell, determines reactivity.
- Ion — Atom with a net electric charge due to electron loss or gain.
- Conductor — Material allowing free movement of electrons.
- Insulator — Material restricting electron movement.
- Coulomb (C) — SI unit of electric charge.
- Ampere (A) — SI unit of electric current.
- Electric Current (I) — Rate of flow of electric charge.
Action Items / Next Steps
- Watch the next video on Coulomb's Law and electric field.