Electrical Current Explained - AC DC, fuses, circuit breakers, multimeter, GFCI, ampere

Understanding Electrical Current

Introduction to Electrical Current

• Paul introduces the topic of electrical current, explaining its significance in understanding electricity and circuits.

• He describes electrical current as the flow of electrons in a circuit, emphasizing the need for electrons to move in a consistent direction.

Conductors and Insulators

• Copper is highlighted as an excellent conductor due to its loosely bound outer electrons, which facilitate easy movement within the metal.

• Rubber is mentioned as an insulator that prevents free electron movement, ensuring electricity remains contained within wires.

Voltage and Electron Flow

• Voltage is defined as the pushing force that drives electron flow, likening it to pressure in a water pipe; higher voltage results in more electron flow.

• The importance of having a voltage difference across a wire is explained; without it, electrons move randomly and do not constitute current.

Measuring Current

• A battery creates a voltage difference that forces electrons to flow uniformly through a circuit.

• The concept of current is introduced, measured in amperes (amps), with practical examples like fuses rated for specific currents discussed.

Conventional Current vs. Electron Flow

• The distinction between conventional current (flow from positive to negative) and actual electron flow (from negative to positive) is introduced.

• Historical context provided by Benjamin Franklin's experiments leads to misconceptions about electric charge accumulation being labeled as positive or negative.

Evolution of Understanding Electricity

• Joseph Thompson's discovery of electrons clarified that they actually flow opposite to what was conventionally believed.

• Despite knowing the true direction of electron flow, conventional current terminology persists due to historical precedent and practicality in engineering formulas.

Practical Implications for Engineers

• Engineers continue using conventional current assumptions when designing circuits despite understanding actual electron behavior.

Understanding AC and DC Electricity

Basics of AC and DC

• The laptop charger requires an input of 100-240 volts and 1.5 amps of alternating current (AC), converting it to an output of approximately 19.5 volts and 3.33 amps of direct current (DC).

• AC electricity alternates direction, while DC flows in one direction only, similar to water flowing down a river.

• AC is primarily used for long-distance electricity transport due to its efficiency in voltage transformation using transformers.

Applications of AC and DC

• High voltage DC transmission lines exist but are less common; DC is mainly used in small electronic devices like laptops and mobile phones.

• Appliances often use both types: washing machines utilize AC for motors but rely on DC for circuit boards controlling settings.

Conversion Between AC and DC

• Rectifiers convert AC to DC, while inverters do the opposite; these conversions are essential in various electronics, including solar power systems.

Measuring Current

• Current flow can be compared to water flow; if too much current exceeds a cable's capacity, it can lead to failure or damage.

• An ammeter measures current flow in amperes (amps), where one amp equals one coulomb per second—approximately six quintillion electrons.

Practical Examples with Circuits

• To power a 1.5-watt lamp with a 1.5 volt battery requires a current of 1 amp, equating to the flow of about six quintillion electrons per second.

• The brightness of lamps varies with voltage; decreasing voltage reduces electron flow, dimming the light.

Series vs Parallel Circuits

• In series circuits, adding resistance decreases overall current; two lamps each with 1 ohm resistance yield lower total current than one alone.

Understanding Current Flow and Resistance in Circuits

Current Distribution in Circuit Branches

• In a circuit with two branches, lamp A receives 1.5 amps while lamp B receives 0.5 amps; however, lamp B appears dimmer due to higher resistance impeding electron flow.

• Resistors can be added to circuits to limit current flow; they create difficulty for electrons, similar to kinks in a pipe that restrict water flow.

Energy Loss and Voltage Drop

• As electrons collide with the resistor material, energy is lost resulting in a voltage drop; this wasted energy is released as heat.

• For example, an LED rated for 22 milliamps connected to a 9V supply requires careful selection of resistors (100 ohm vs. 450 ohm) to avoid burning out or underperformance.

Measuring Electrical Consumption

• Affordable energy meters are available for measuring voltage, current, and energy consumption of home appliances; these tools help track running costs effectively.

Fuses and Circuit Protection

• Fuses contain thin wires rated for specific currents (e.g., 3 amps); if exceeded, the fuse burns out to protect components by breaking the circuit.

• Fuses serve as weak points in circuits and are commonly found on circuit boards or built into plugs for safety.

Circuit Breakers: Overload and Short Circuit Protection

• Circuit breakers act as automatic switches that open when excessive current flows due to overload or short circuits; they provide essential protection by cutting power.

• Modern circuit breakers include features like short circuit protection which detects instant surges in current caused by direct contact between positive and negative wires.

Ground Fault Protection Devices