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Chapter 2: Basic Electronics and Units of Measure Introduction This chapter lays the foundation for your electronics career. This unit introduces you to the fundamental concepts, terms, and units of measures common to all electronics technology.

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Chapter 2 l.jpg

Chapter 2:

Basic Electronics and Units of Measure


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Introduction

  • This chapter lays the foundation for your electronics career.

  • This unit introduces you to the fundamental concepts, terms, and units of measures common to all electronics technology.

  • The material presented forms the basis for all subsequent studies in electronics.

Chapter 2 - Basic Electronics and Units of Measure


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Atomic Structure

  • All matter is composed of increasingly smaller building blocks. Those building blocks are:

Chapter 2 - Basic Electronics and Units of Measure


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Atomic Structure

Chapter 2 - Basic Electronics and Units of Measure


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Atomic Structure Terms

  • Electrons: Minute mass compared to protons and neutrons. Under normal conditions, an atom has equal numbers of electrons and protons.

  • Shell: Allowable orbit level of electrons. There are a fixed number of electrons in any given shell.

  • Free electron: An electron with sufficient energy to break away from its parent atom.

  • Valence electron: An electron in the outermost orbit of an atom.

  • Ion: An atom that has lost or gained an electron. An atom that has lost an electron is a positive ion; an atom that has gained an electron is a negative ion.

Chapter 2 - Basic Electronics and Units of Measure


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Classes of Materials

  • Materials can be classified by their ability to pass electrical current.

    • Insulators: Materials that have few free valence electrons and do not conduct electricity well.

    • Conductors: Materials with loosely bound valence electrons where little energy is required to free them.

    • Semiconductors: Materials that are neither good insulators nor good conductors. Typical semiconductors have four valence electrons and are represented by germanium and silicon.

    • Superconductors: Materials that offer no opposition to current flow, essentially being perfect conductors.

  • The charge of a material is determined by having more or fewer electrons than protons. Materials with an excess of electrons are negatively charged. Materials with a deficiency of electrons are positively charged.

Chapter 2 - Basic Electronics and Units of Measure


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Attraction and Repulsion by Charges

  • Like charges repel each other. Unlike charges attract each other.

Chapter 2 - Basic Electronics and Units of Measure


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Unit of Measure for Charge

  • Charge is measured in coulombs (C).

  • One coulomb is equal to the charge of caused by the accumulation or deficiency of 6.25 x 1018 (6,250,000,000,000,000,000) electrons.

  • The symbol for charge is Q.

Chapter 2 - Basic Electronics and Units of Measure


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Voltage

  • When some distance separates two bodies with unequal charges, there is the potential for doing work.

  • The difference in charge between any two points is referred to as a difference in potential.

  • Potential difference is measured in terms of voltage. The unit of measure is the Volt (V).

  • Electromotive Force (emf) is the potential difference that remains between points while charges are being transferred.

Chapter 2 - Basic Electronics and Units of Measure


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Current Flow

  • Copper has 29 electrons in its outer orbit. At room temperature, enough thermal energy is present to ionize many of the copper atoms, giving copper an abundance of free electrons.

  • When opposite charges are placed upon the ends of the copper wire, the EMF causes the electrons to flow.

  • Current flows from negative to positive potentials (called electron current flow). In some cases, current flow is represented as the movement of positive charges. This is called conventional current flow.

Chapter 2 - Basic Electronics and Units of Measure


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Unit of Measure for Current

  • Current is the movement of charges in a conductor.

  • It is the measure of the number of electrons that flow past a given point per second.

  • One Ampere (A) is the amount of current that flows when one coulomb (Q) flows past a point in one second.

  • This is expressed by the equation:

Chapter 2 - Basic Electronics and Units of Measure


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Resistance

  • Current flowing through a circuit encounters opposition.

  • This opposition is referred to as resistance.

  • For current to flow in a circuit, an EMF must be applied that overcomes this opposition.

  • The unit of measure for resistance (R) is measured in ohms ()

  • The practical range of resistance values used in electronics extends from thousandths of ohms (milliohms) to millions of ohms (megohms).

Chapter 2 - Basic Electronics and Units of Measure


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Ohm’s Law

  • The most important principle in electronics is Ohm’s Law.

  • Georg Simon Ohm expressed the relationship between current, voltage, and resistance in 1827 and this principle bears his name.

  • Ohm’s Law states that: the current that flows in a circuit is directly proportional to the voltage across the circuit and is inversely proportional to the resistance in the circuit.

  • It is expressed mathematically by:

or

Chapter 2 - Basic Electronics and Units of Measure


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Current is Proportional to Voltage

  • The higher the voltage applied to a circuit, the greater the current will be.

Chapter 2 - Basic Electronics and Units of Measure


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Current versus Resistance

  • Current is inversely proportional to resistance

  • See this slide and the following slide for examples

Chapter 2 - Basic Electronics and Units of Measure


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Current versus Resistance

Chapter 2 - Basic Electronics and Units of Measure


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Alternate Forms of Ohm’s Law

  • Ohm’s law may be rearranged to solve for resistance or voltage.

  • From

  • We can get:

  • And:

Chapter 2 - Basic Electronics and Units of Measure


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Electrical Power

  • Electrical power is a measure of the rate at which energy is used and is measured in watts.

  • All electrical devices dissipate power.

  • Based on Ohm’s Law, power calculations are

    P = IV

  • Other variations include:

    P = I2R and P = V2/R

Chapter 2 - Basic Electronics and Units of Measure


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Conductance

  • Conductance is the inverse of resistance.

  • It expresses how readily current can flow through a material.

  • The unit of measure for conductance (G) is siemens (S). At one time, the unit of measure was called mhos.

  • The relationship between resistance and conductance is expressed by G = 1/R

Chapter 2 - Basic Electronics and Units of Measure


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Electrical Quantities, Abbreviations, Units, and Symbols

Chapter 2 - Basic Electronics and Units of Measure


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Electrical Quantities, Abbreviations, Units, and Symbols

Chapter 2 - Basic Electronics and Units of Measure


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Mechanical Quantities

  • Practical electronic systems often measure and/or control mechanical quantities.

  • Terms associated with mechanical quantities are:

    • Force: Any action on an object that tends to change its position in a specific direction.

    • Pressure: Force distributed over an area, P=F/A.

    • Position

    • Velocity and Speed: Speed is a measure of how fast an object changes position without regard to direction; velocity implies movement in a specific direction.

    • Acceleration: Describes the rate of change of speed (or velocity).

Chapter 2 - Basic Electronics and Units of Measure


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Light and Other Waves

  • Light plays a critical role in many electronic and electromechanical systems.

    • Distinguishing between presence or absence of light

    • Brightness

    • Color

  • Optoelectronics refers to the use of optical (light) devices in electronic systems.

  • Acoustical waves are measured in decibels. Intensity of a sound wave is a measure of how loud it is.

Chapter 2 - Basic Electronics and Units of Measure


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Wavelength and Frequency

  • The color of visible light and the tone (pitch) of a sound wave is determined by frequency.

  • The inverse of frequency is wavelength.

  • All waves exhibit common properties.

Chapter 2 - Basic Electronics and Units of Measure


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Wavelength and Frequency

  • A wave consists of repetitive peaks (crests) and valleys (troughs).

  • Wave velocity is determined by the medium and the characteristics of the wave.

  • Wavelength is the physical distance between corresponding points on two consecutive waves.

  • The period of a wave is the time required for one complete cycle.

  • The reciprocal of a wave’s frequency is its period.

Chapter 2 - Basic Electronics and Units of Measure


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Magnetism and Electromagnetism

  • Magnetic and electromagnetic fields play important roles and are fundamental to electronic and electromechanical systems.

  • Motors, generators, speakers, microphones, computer storage devices, and many more devices are based upon magnetic/electromagnetic principles.

Chapter 2 - Basic Electronics and Units of Measure


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Magnetic Fields

  • Surrounding all magnetic objects is an invisible, but measurable field.

  • A magnetic field is the region around a magnet where another magnet would experience interaction.

Chapter 2 - Basic Electronics and Units of Measure


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Magnetic Flux

  • The lines around a magnet are called lines of flux or magnetic flux lines.

  • Each flux line is elastic, but continuous.

  • Flux lines never touch or intersect one another.

  • The unit of magnetic flux is the weber.

  • One weber is equal to 100,000,000 flux lines.

  • The symbol for magnetic flux is  .

Chapter 2 - Basic Electronics and Units of Measure


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Magnetic Poles

  • The regions in a magnet where the external flux lines are most concentrated are called the poles of the magnet.

  • The poles of a magnet will attempt to force the magnet to align with the earth’s magnetic fields.

  • The north-seeking pole is referred to as the north pole and the south-seeking pole is referred to as the south pole.

  • Like magnetic poles repel one another; unlike poles attract.

Chapter 2 - Basic Electronics and Units of Measure


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Flux Density

  • Flux Density is the measure of how many flux lines appear in a certain area.

  • The unit of measurement for flux density is the tesla (T).

  • One tesla corresponds to a flux density of one weber per square meter.

Chapter 2 - Basic Electronics and Units of Measure


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Magnetic Domains

  • Materials that can be magnetized have regions called magnetic domains.

  • Each magnetic domain acts like a miniature bar magnet. The length of a domain is only a fraction of a millimeter.

  • It takes energy to rotate or change the orientation of magnetic domains. This energy loss is often evidenced as heat in electromagnetic devices.

Chapter 2 - Basic Electronics and Units of Measure


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Magnetomotive Force

  • Magnetomotive Force (mmf) refers to the energy source that actually creates the flux; it is the magnetic equivalent of electromotive force.

  • The symbol for magnetomotive force is .

  • The unit of measure is ampere-turns (A•t).

Chapter 2 - Basic Electronics and Units of Measure


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Magnetizing Force

  • Magnetizing force (H), also called magnetic field intensity, is closely related to the magnetomotive force but includes a physical dimension.

  • The unit of measure for magnetizing force is ampere-turns per meter (A•t/m).

  • Reluctance is the magnetic equivalent of resistance. Reluctance opposes the passage of magnetic flux.

  • The symbol for reluctance is , and the unit of measure is A•t per weber.

Chapter 2 - Basic Electronics and Units of Measure


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More Magnetism Terms and Units

  • Ohm’s Law for magnetic circuits:

  • Permeability is the ability of a a material to pass magnetic flux. Its symbol is .

Chapter 2 - Basic Electronics and Units of Measure


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Magnetic versus Electromagnetic Fields

  • Many electrical devices use temporary magnets for their operation. These magnets exhibit magnetic characteristics as long as they’re under the influence of a magnetizing field.

  • Temporary magnets generally rely on the flow of electrons through a conductor to create the magnetizing field.

  • The direction of magnetic fields is determined by the direction of current flow in a conductor.

Chapter 2 - Basic Electronics and Units of Measure


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