Electricity Recap Lecture

Static Electricity

• Definition: A charged object has static electricity, experienced when the object is discharged.
• Charge Types: Positive and negative, originating from electrons.
• Electrons:
  • Orbit the nucleus in shells.
  • Carry negative charge and can become free to move.

Conductors and Insulators

• Metals: Composed of positive ions surrounded by free electrons.
• Example: Rubbing a polythene rod with a cloth transfers electrons to the rod, making it negatively charged, and the cloth positively charged.
• Key Principles:
  • Like charges repel; opposite charges attract.
  • Demonstrated by suspended rods and rubbing methods (polythene vs cellulose acetate rod).

Applications

• Electrostatic Painting:
  • Paint particles are charged to repel each other for an even coat.
  • Oppositely charged surfaces attract charged paint particles.
• Lightning:
  • A cloud becomes negatively charged; the pathway to Earth becomes ionized, allowing discharge.
• Safety Concerns:
  • Static electricity in power lines can pose risks (e.g., kite flying near pylons).

Current Electricity

• Definition: Flow of electric charge.
• Conductors:
  • Good conductors: copper, silver, steel, aluminum.
  • Insulators: wood, paper, rubber.
  • Semiconductors: silicon, germanium (partial conductors).

Current Flow

• Direction: Historic convention states positive to negative, although electron flow is negative to positive.
• Circuit Components:
  • Cells, batteries, switches, bulbs, ammeters, voltmeters, diodes, resistors.
  • Ammeters measure current (amperes), voltmeters measure voltage (volts).

Units and Measurements

• Charge (Coulombs): Unit 'C', e.g., 5 C.
• Current (Amperes): Unit 'A', e.g., 5 A.
• Conversions:
  • 1 Amp = 1000 milliamps = 1,000,000 microamps.
  • Metric prefixes: milli (10^-3), micro (10^-6), nano (10^-9).

Resistance

• Definition: Opposition of a conductor to current.
• Factors Influencing Resistance:
  • Temperature increases resistance due to more collisions (kinetic theory).
  • Longer wires result in more potential collisions, thus more resistance.
  • Thicker wires have lower resistance due to more pathways for electrons.

Ohm's Law

• Expression: Current is proportional to voltage if temperature remains constant.
  • Equation: V = I × R
    • V: Voltage
    • I: Current
    • R: Resistance (measured in ohms).
• Measurement Setup:
  • Voltmeter in parallel, ammeter in series.
  • Variable resistors adjust resistance in circuits.

Remember to review the principles of static and current electricity, with emphasis on the behavior of electrons, applications of static electricity, and the fundamentals of circuit components and Ohm's Law.