Overview
This lecture introduces electric current, focusing on how moving electric charges (electrons or ions) create current in conductors like metals and electrolytic solutions.
Charge and Electrostatics
- There are two types of electric charge: positive and negative.
- Like charges repel; unlike charges attract.
- Electrostatic interactions are the basis for electric forces between charged particles.
Structure of Copper and Electrical Conductors
- Copper atoms have 29 protons and 29 electrons, with one loosely held outer electron.
- The outermost electron in copper can move freely, making copper a good electrical conductor.
- Silver has a similar electron arrangement, also making it a good conductor.
Electric Current in Metal Wires
- Connecting a battery to a copper wire causes electrons to move from the negative side toward the positive side.
- As electrons move, they leave behind positive charges, which the battery replenishes.
- Electric current is the movement of charge; specifically, the flow of electrons in metals.
Measuring Electric Current
- Current is quantified by placing an imaginary boundary in the conductor and counting the amount of charge passing through per second.
- The direction of conventional current is the direction positive charges would move (opposite electron flow in metals).
- Current is analogous to water flow in a river.
Electric Current in Salt Water (Electrolytes)
- Pure water does not conduct electricity, but adding table salt (NaCl) dissociates into Na⁺ and Cl⁻ ions.
- When a battery is connected to salt water, Na⁺ ions move toward the negative terminal, and Cl⁻ ions move toward the positive terminal.
- Current in electrolytes is due to movement of both positive (Na⁺) and negative (Cl⁻) ions in opposite directions.
- The total current is the sum of charges passing through a boundary per second, regardless of their direction.
Key Terms & Definitions
- Charge — a property of matter that causes it to experience a force in an electric field; can be positive or negative.
- Conductor — material that allows easy movement of electric charge (e.g., copper, silver).
- Electric current (I) — the rate of flow of electric charge, measured in coulombs per second (amperes).
- Electrolyte — a substance containing free ions that conducts electricity in solution.
- Ion — a charged atom or molecule (e.g., Na⁺, Cl⁻).
Action Items / Next Steps
- Review the definitions of charge, electric current, conductor, and electrolyte.
- Practice drawing diagrams showing electron and ion movement in circuits.