Electrical Principles: Charge and Current

• Study notes for Unit 4, Electrical Principles and Technologies, Topics 1 and 2

Topic 1 Definitions

• Charge separation: The build-up of opposite electrical charges on different objects or parts of an object
• Electrical discharge: The release and transmission of built-up static electrical energy
• Electrical current: The continuous flow of electric charge through a conductor
• Circuit: A closed path that allows electric current to flow
• Electrical energy: Energy caused by the movement of electrons
• Ampere: The standard unit for measuring electric current
• Short Circuit: A low-resistance connection between two points in an electrical circuit, resulting in excessive current flow
• Electrochemical cell: A device that converts chemical energy into electrical energy
• Electrolyte: A substance that conducts electric current as a result of dissociation into ions when dissolved in a solution
• Electrolysis: Using electrical current to drive a non-spontaneous chemical reaction

Topic 1 Knowledge

• An electron has a negative charge
• A proton has a positive charge
• A balloon sticks to the wall due to charge separation and the attraction of opposite charges
• The Laws of Electrical Charges state that like charges repel, and opposite charges attract
• A conductor allows electric current to flow easily, while an insulator resists the flow of electric current
• Examples of conductors include metals like copper and aluminum; examples of insulators include rubber, plastic, and glass.
• Voltage is the electrical potential difference, measured in volts, and a voltmeter measures voltage
• A minimum of a source of energy, a conductor, and a load (something to use the energy) is needed to complete a circuit
• Electrical safety practices include using insulated tools, avoiding water, and not overloading circuits
• Fuses and circuit breakers protect circuits from overcurrent by breaking the circuit when the current exceeds a safe level
• Lightning rods protect buildings by providing a path for lightning to reach the ground safely
• A dry cell uses a paste electrolyte, while a wet cell uses a liquid electrolyte
• A rechargeable battery can be recharged by reversing the chemical reactions that occur during discharge
• A primary cell is non-rechargeable, while a secondary cell is rechargeable
• Electroplating is the process of coating a metal object with a thin layer of another metal using electrolysis

Topic 2 Definitions

• Resistance: The opposition to the flow of electric current, measured in ohms
• Ohm’s Law: States that the voltage across a conductor is directly proportional to the current flowing through it, with the constant of proportionality being the resistance (V = IR)
• Ohm’s Calculations: Using Ohm’s Law (V=IR) to calculate voltage, current, or resistance in a circuit
• Voltmeters: Instruments used to measure voltage in a circuit
• Ammeters: Instruments used to measure current in a circuit
• Schematic: A diagram that uses symbols to represent the components and connections in an electrical circuit
• Series Circuit: A circuit in which components are connected end-to-end along a single path
• Parallel Circuit: A circuit in which components are connected across each other, providing multiple paths for the current to flow
• Transistors: Semiconductor devices used to amplify or switch electronic signals and electrical power
• Microcircuits: Integrated circuits (ICs) with many transistors and other components on a single chip

Topic 2 Knowledge

• In an insulator, electrons are tightly bound and do not move freely
• In a conductor, electrons are free to move and carry electric charge
• A resistor has a fixed resistance, while a variable resistor (potentiometer) allows the resistance to be adjusted
• Examples of resistors include those found in electronic devices; variable resistors can be found in volume controls or light dimmers
• A waterfall is used as a model of electricity: the height of the waterfall represents voltage, the rocks represent resistance, and the water flow represents current
• Ohm’s Law (V=IR) can be used to calculate voltage, current, or resistance if two of the values are known
• A multimeter measures voltage, current, and resistance
• Schematic diagrams use specific symbols for each component (e.g., resistor, battery, switch) and lines to represent wires
• Proper symbols must be used when drawing schematic diagrams to correctly represent circuit components
• If loads are added to a series circuit, the total resistance increases
• If loads are added to a parallel circuit, the total resistance decreases
• Combination circuits in a house use parallel circuits to deliver voltage to appliances and lights
• Christmas lights can be wired in series or parallel, with parallel being more reliable because if one bulb burns out, the rest stay lit