1 Fundamentals of Electricity, Magnetism, and Electronics

Learning Objectives Describe the structure of an atom. Explain the relationship between free electrons and current flow. Summarize the three basic units of electrical measurement. Describe the characteristics of series, parallel, and series-parallel circuits. Recall and apply Ohm’s law.

Learning Objectives Explain the relationships between magnetism and electricity. Explain the construction and operation of diodes, transistors, and silicon controlled rectifiers.

Matter, Elements, and Atoms Matter is anything that takes up space and has mass Composed of elements An element cannot be changed into simpler material by chemical means An atom is smallest particle of an element that can exist

Atoms Consist of protons, neutrons, and electrons Structure of atom determines properties of an element

Electrons Travel in orbits around center of atom Number per atom varies from one element to another Identical in all elements Have negative (-) electrical charge

Protons and Neutrons Bound together in the nucleus of atom Protons are positively charged Larger and heavier than electrons Neutrons are electrically neutral

Characteristics of Atoms All atoms have equal number of protons and neutrons Electrically neutral Held together because unlike electrical charges attract Positively charged protons hold negatively charged electrons in their orbits

Characteristics of Atoms In most atoms, nucleus is surrounded by bound electrons Elements that contain atoms with bound electrons are insulators In some atoms, nucleus is surrounded by free electrons Elements that contain atoms with free electrons are conductors

Atoms and Electricity Movement of free electrons will only occur when there is a complete circuit and a difference in electrical potential is produced by the source of electricity Movement of free electrons is electric current

Producing Electricity Electricity is produced in three ways Mechanically Chemically Statically

Direct and Alternating Current Direct Current (DC) Produced by battery Found in most small engine circuits Alternating Current (AC) Changes direction Produced by alternator

Electrical Units of Measure Ampere (A) Number of electrons flowing past a given point in a circuit in a specific length of time One ampere is 6,240,000,000,000,000,000 electrons flowing past a given point per second Volt (V) Difference in potential between two points Ohms (Ω) Resistance to electron flow

Ohm’s Law Used to calculate unknown circuit value when other two values are known Formula I = E/R where: I = Amperes E = Volts R = Ohms

Ohm’s Law Cover unknown value and perform calculations indicated by remaining values

Circuit Components Source of electricity Load Conductors Battery or alternator (generator) Load One or more pieces of electrical equipment Conductors Connect source to load

Circuit Types Series circuit Parallel circuit Series-parallel circuit One path for current Parallel circuit More than one path for current Series-parallel circuit Some devices connected in series and others connected in parallel

Series Circuit

Series Circuit Rules Sum of voltage drops around circuit is equal to source voltage Voltage drop is decrease in voltage as current passes through a resistance Current is the same in all parts of circuit The sum of the individual resistances in circuit equals total resistance of circuit

Parallel Circuit

Parallel Circuit Rules Voltage is same in all parts of circuit Total resistance is always less than smallest resistance Formula for total resistance: 1/Rt = 1/R1 + 1/R2 + 1/R3… Total current is sum of currents from each current branch Formula for total current: It = E ÷ Rt

Series-Parallel Circuit

Series-Parallel Circuit Rules Determine resistance of each parallel element in circuit Plug this resistance into circuit so circuit can be treated as series circuit

Magnetism Magneto systems use magnets to generate electricity needed to fire spark plugs All magnets produce a magnetic field Magnetic field is strongest close to magnet Field leaves north pole and reenters south pole

Theory of Permanent Magnets Electron moving in fixed circular orbit creates magnetic field Multiple orbiting electrons form domains Domains scattered in random patterns in unmagnetized material Under influence of strong external magnetic field, domains become aligned and total material is magnetized

Theory of Permanent Magnets

Properties of Magnets Soft iron loses magnetic effect as soon as it is removed from magnetic field Hard steel retains magnetic characteristics indefinitely Magnetic lines of force seem to penetrate all substances

Magnetic Attraction and Repulsion Lines of forces leaving the north pole of one magnet will enter the south pole of an adjacent magnet Lines leaving similar (like) poles are repelled

Magnetism and Electricity When magnetic lines of force are cut by a wire, electricity will flow in the wire When electrons flow through a conductor, a magnetic field develops around the conductor When current in conductor increases, the strength of magnetic field increases

Electrical Wire Metal conductor encased in plastic insulation Solid or stranded Diameter of conductor determined by amount of current it is intended to carry Wire diameter and length determine the resistance of the wire Wire and cable sizes expressed by a gauge number