Current Electricity and Circuits

Electric Current and Circuits

  • Direct Current (DC)

    • Current flows in one direction.

    • Constant flow of charge.

  • Alternating Current (AC)

    • Current flows back and forth, changing direction 60 times per second (60Hz).

Current Electricity

  • Flow of charges from high potential to low potential (voltage).

  • A "pump" creates a potential difference.

  • Devices using current create resistance, slowing charge flow.

  • A closed circuit is necessary for current to flow.

  • Circuits can be visualized with symbols.

Voltage, Current, and Resistance

  • Voltage (V)

    • Indicates potential difference (like pressure).

    • Unit: Volt (V), named after Count Alessandro Volta.

  • Current (I)

    • Flow rate of charge (how fast).

    • Unit: Ampere (Amps, A), named after Andre Ampere.

    • 1 Coulomb per second.

  • Resistance (R)

    • Slowing of charge flow.

    • Unit: Ohm (Ω), named after Georg Ohm.

    • Present when 1 ampere of current flows under 1 volt potential difference.

    • Affects based on size, material, and temperature.

Resistance and Ohm's Law

  • Ohm's Law states that resistance is constant regardless of the voltage applied.

  • Insulators have high resistance; conductors have low resistance.

Device Resistance Factors

  • Wire Resistance

    • Thickness: Thicker wire = Less resistance.

    • Length: Longer wire = More resistance.

    • Temperature: Higher temperature = More resistance.

    • Material types affect resistance: Au < Cu < Fe < Al.

  • Potentiometer: A variable resistor with a long coil of wire.

Circuit Configurations

  • Series Circuit

    • Current has one path to travel.

    • If one element fails, the circuit opens.

  • Parallel Circuit

    • Current has multiple paths.

    • If one path fails, others remain closed allowing current to flow.

Voltage, Current, and Resistance Review

  • Voltage is potential difference (pressure).

  • Current is charge flow (flow rate).

  • Resistance is the opposition to charge flow.

Nikola Tesla vs. Thomas Edison

  • Tesla: Innovator in renewable energy; focused on people.

  • Edison: Businessman; operated for profit.

Elements of a Circuit Diagram

  • Battery/Cell: Source of charge, 'pump'.

  • Resistor: Slows charge travel.

  • Lamp/Motor: Uses electricity; resistance.

  • Capacitor: Stores/releases charge.

  • Switch: Opens/closes circuit.

  • Ground: Low potential source.

Reading Resistors: Color Code

  • Standard Resistor Color Bands

    • First two bands: first two digits of resistance.

    • Third band: multiplier (x1 to x1,000,000).

    • Fourth band: tolerance (Red=2%, Gold=5%, Silver=10%, none=20%).

Resistance and Voltage in Series Circuits

  • Total resistance: sum of each element's resistance.

  • Total voltage: sum of voltage drops across elements.

Resistance in Parallel Circuits

  • Adding paths decreases overall resistance.

  • Total resistance formula: sums of reciprocals of individual resistances.

Current in Parallel Circuits

  • Total current = sum of currents through elements.

  • Voltage across each branch is the same (equal to IR).

Important Circuit Devices

  • Fuse: Breaks circuit if current exceeds limit.

  • Circuit Breaker: Can be reset, uses a spring-loaded arm or electromagnet.

Commercial Electricity

  • Energy purchased from power companies in kilowatt-hours (kWh).

  • A unit of energy = energy transferred in 1000 watts for one hour.

  • Voltage over power lines is around 14,000 V, stepped down to household use (110V or 220V) by transformers.