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Electronics > Fundamentals of Electricity > Flashcards

Fundamentals of Electricity Flashcards

1
Q

Matter

A
  1. Occupies space
  2. Has weight
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2
Q

Elements

A
  1. Basic building block of nature
    2.Can not be reduced to a simpler substance by chemical means
  2. Over 100 known elements
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3
Q

Parts of an atom

A
  1. Nucleus: located at the centre of the atom, it is a place
  2. Protons: Positively charged particles inside the nucleus
  3. Neutrons: Uncharged particles inside the nucleus
  4. Electrons: Negatively charged particles that orbit the nucleus
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4
Q

Size of protons and electrons

A

Imagine a cathedral
In the middle, there is a grapefruit, that is roughly the size of protons and neutrons. And electrons would be like a laser point around the out walls

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5
Q

Atomic number

A

The number of protons in the nucleus of the atom
Each element has its unique number of protons

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6
Q

Atomic weight

A
  • The mass of an atom
  • Determined by the total number of protons and neutrons in the nucleus.
    Each element has its unique weight
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7
Q

Shell

A
  • Electrons orbit here
  • Concentric circles around nucleus
  • Filled in sequence
  • Label from K to Q
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8
Q

Valence Shell

A

The outermost shell, the Q shell

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9
Q

Valence

A

The number of the electrons contained in the valence shell

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10
Q

Conductors

A
  • Materials that contain a large number of free electrons
  • 3 or fewer electrons in the valence shell is potentially a good conductor
    High to low
    Silver > Copper > Gold (least oxidized) > Aluminum > Tungsten > Iron > Nichrome
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11
Q

Insulators

A
  • Prevent the flow of electricity
  • Stabilized by absorbing valence electrons
    Mica > Glass > Teflon > Paper(Paraffin) > Rubber > Bakelite > Oil > Procelain > Air
    5 or more electrons in the valence shell
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12
Q

Semiconductors

A
  • Can be altered to function as either a conductor or insulator
    4 electrons in the valence shell
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13
Q

Negative and positive Ion

A

A negatively charged or positively charged atom

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14
Q

Ionization

A

The process of gaining or losing electrons
Significant in current flow
e.g rubbing something to get static electric

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15
Q

Current

A

Movement of electrons from negatively charged atoms to positively charged atoms at the speed of light.
Represented as I

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16
Q

Coulomb

A

Unit adopted for measuring charges
6.24 * 10 18 electrons
Represented as C

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17
Q

Ampere

A

One coulomb moving past a single point in one second
Named for French Physicist Andre Marie Ampere
Current measured in ampers
Represented by A

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18
Q

Potential

A

The ability of the source to perform electrical work

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19
Q

Difference of Potential

A
  • Causes electrons to move or flow in a circuit
  • Referred to as electromotive force (emf) or voltage
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20
Q

Voltage

A
  • The force that moves the electrons in the circuit
  • The pressure or pump that moves electrons
  • Represented by E or V
  • Unit of measure called the volt
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21
Q

Resistance

A
  • Opposition to the flow of electrons
  • Degree of resistance depends on size, shape or temperature
  • Measured in Ohms, named for George Simon Ohm
  • Represented by Greek letter Omega Ω
    Everything has resistance, except super conductors
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22
Q

First low of electrostatic charges

A

Like charges repel each other

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23
Q

Second law of electrostatic charges

A

Unlike charges attract each other

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24
Q

The relationship between amperes and coulombs pers second can be expressed as

A

I = Q / t
I = current measured in amperes
Q = quantity of electrical charge in coulombs
t = time in seconds

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25
Q

Hole

A

The movement of an electron from one atom to the next, creating the appearance of a positive charge moving in the opposite direction

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26
Q

Flow

A

Negative to Positive: electron flow and current flow
Positive to Negative: hole flow

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27
Q

Voltage source

A
  • Supplies electrons from one end of the conductor
  • Removes electrons from the other end of the conductor
  • Can be thought of as a kind of a pump
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28
Q

Voltage sources

A
  • Friction
  • Magnetism
  • Chemicals
  • Light
  • Heat
  • Pressure
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29
Q

Voltage sources - Friction

A

Van de Graaff generator, lightning storm

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30
Q

Voltage sources - Magnetism

A
  • Most common method of producing electrical energy
  • Produced using a generator
  • Powered by steam from nuclear power or coal, water, wind or gasoline or diesel engines.
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31
Q

Voltage sources - Chemicals

A
  • Cell (1.5 V)
  • Second most popular method of producing electrical energy
  • Consists of two metals
    • Copper
    • Zinc
  • Many cells can be connected to form a battery
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32
Q

Voltage sources - Light

A
  • Photovoltaic cell
  • A single cell can produce a small voltage
  • Many cells must be linked to produce a usable voltage and current
  • Primarily used in satellites and cameras
  • Cost is high but is declining
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33
Q

Voltage sources - Heat

A
  • Thermocouple
  • Two dissimilar wires twisted together
  • Voltage is directly proportional to the amount of heat applied
  • Used in thermometers
  • Also called a pyrometer
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34
Q

Voltage sources - Pressure

A
  • Piezoelectric effect
  • Voltage is small; must be amplified to be useful
  • Used in crystal microphones, phonograph pickups (crystal cartridges) and precision oscillators
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35
Q

Direct current

A

Electrons flow in only one direction

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36
Q

Alternating current

A

Electrons flow in one direction then in the opposite direction

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37
Q

Battery

A

A combination of two or more cells

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38
Q

Primary cells

A
  • Cells that can not be recharged
    • Leclanche cell or dry cell; also referred to as a carbon-zinc cell
    • Alkaline cell
    • Lithium cell (last longer)
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39
Q

Secondary cells

A
  • Cells that can be recharged
    • Lead-acid battery or wet cell
    • Nickel- Cadmium cell or Ni-Cad
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40
Q

Connecting Cells and Batteries

A
  • Series
    • Series
      • It = I1 = I2 = I3 (current)
      • Vt = V1 + V2 + V3
    • Series opposing
      • Little practical value
  • Parallel
    • It = I1 + I2 + I3
    • Vt = V1 = V2 = V3
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41
Q

Voltage rise and drop

A

Voltage rise: Potential energy or voltage introduced into a circuit
Voltage drop: The energy given up as electrons encounter resistance in the circuit

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42
Q

Ground

A
  • Earth
    • Used to prevent electric shock.
  • Electrical
    • Provides a common reference point.
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43
Q

Resistance

A
  • Opposition to electron flow in a circuit
    • Expressed by the symbol R
    • Measured in ohms
    • Abbreviated with Greek symbol Ω
    • Varies from material to material
      • Silver is the best
      • Copper is the most common
      • Gold doesn’t tarnish
    • Affected by temperature
    • Affected by the size diameter of the conductor
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44
Q

Resistivity

A

The resistance of a material to current flow
- Resistivity is different for different materials
- Even good conductors have different levels of resistivity
Compare everything to silver

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45
Q

Conductance

A
  • The ability of a material to pass electrons
    • Expressed as G
    • Unit known as Mho (ohm backwards)
    • Abbreviated with the inverted Greek symbol ℧
  • is derived by
    R = 1/G or G = 1/R
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46
Q

Resistors

A
  • Components manufactured to possess a specific value of resistance to the flow of current
  • Come in two classifications:
    • Fixed value
    • Variable
  • Variety of shapes and sizes to meet specific circuit, space and operating requirements
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47
Q

Tolerance

A
  • The amount that the resistor may vary and still be acceptable
  • The larger the tolerance the cheaper it is to manufacture
  • Resistors are available with tolerances of +-20%, 10%, 5%, 2% and 1%
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48
Q

Molded Carbon resistor

A
  • The most commonly used
  • Inexpensive
  • Manufactured in standard resistor values
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49
Q

Wirewound

A
  • Used in high-current circuits
  • Resistance varies from a fraction of an ohm to several thousand ohms
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50
Q

Film resistors

A
  • Becoming increasingly popular
  • Three types : carbon film, metal film and tin oxide film
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51
Q

Surface mount resistors

A
  • Ideal for small circuit applications
  • Available in both thick and think films
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52
Q

Variable resistors

A
  • Allow the resistance to vary
  • Vary linearly or logarithmically
  • Called a potentiometer when used to control voltage
  • Called a rheostat when used to control current
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53
Q

Resistor identification

A
  • Alphanumeric
  • Example of an alphanumeric code
    • RN60D5112F
      RN60 = Resistor style (composition, wirewound, film)
      D = Characteristics (effects of temperature)
      5112 = Resistance value (2 represents the number of zeros)
      F = Tolerance
  • EIA (Electronic Industries Association) Color code
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54
Q

Resistors in circuits

A
  • Resistors are typically configured in a circuit in one of three different ways
    • Series circuit configuration (voltage divider)
    • Parallel circuit configuration (current divider)
      • 1/Rt = 1/R1 + 1/R2 + … + 1/Rn
      • 1/Rt is always less than the least Rn
    • Compound circuit configuration
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55
Q

Electric circuits

A
  • The path that the current follows is called an electric circuit
  • All electric circuits consist of
    • A voltage source
    • A load (convert energy to different form)
    • A conductor
56
Q

Ohm’s law

A

V = I * R

57
Q

Kirchohoff’s Law

A

In GR Kirchhoff extended Ohm’s Law with two important statement

Kirchhoff’s current law
The Algebraic sum of all the current entering and leaving a junction is equal to zero

Kirchhoff’s voltage law
The Algebraic sum of all the voltages around a closed circuit equals zero

58
Q

Power

A
  • Relates to the rate at which work is being done.
    • Work is done when a force (voltage) causes motion (current)
  • Voltage creates current, causing electrons to move in a circuit
  • The total power dissipated in a series or parallel circuit is equal to the sum of the power dissipated by the individual components
59
Q

Electric power rate

A
  • The instantaneous rate at which work is done
  • Measured in watts
    • Wattage is greater when work is done in a short period of time than when the same amount of work is done in a longer period of time.
60
Q

Watt

A
  • The basic unit of power
  • Equal to the voltage across a circuit, multiplied by the current through the circuit
  • Represents the rate at which work is being done
    P = I * E
    The power dissipated in a circuit is often less than 1 watt
61
Q

Circuit analysis

A

To determine the power dissipated by a component
- Voltage drop times current

62
Q

Voltage Dividers

A

Used to set a bias or operating point of various active electronic components
- Transistors
- Integrated circuits
Used to divide a higher voltage to a lower voltage
Ofen referred to as scaling

63
Q

Current Division

A

Current is directly proportional to the voltage across the circuit
The voltage drop is equal to the percentage of the dropping resistor to the sum of the dropping network
E (drop) = E (source) * R (drop) / R (total)

64
Q

Bleeder Current

A

The current flow into the first component in the circuit to start the voltage division process
Should have 1/10 of the amp of the overall load current (rule of thumb)

65
Q

Magnets

A
  • Natural magnet
    • Derived from magnetite
  • Artificial magnet
    • Created by ribbing a piece of soft iron with a piece of magnetite
  • Electromagnet
    • Created by current flowing through a coil of wire
66
Q

The earth is a huge magnet

A

The north magnetic pole is different from the north geographic pole

67
Q

The colour code for magnets

A

Red for the north pole
Blue for the south pole

68
Q

Magnetism

A

Can be traced to the atom
As electrons orbit the nucleus, they also spin on their axis
This electrostatic charge produces a magnetic field
The direction of the magnetic field is the same as the electron’s direction of spin

69
Q

Ferromagnetic materials

A

Materials that respond to magnetic fields, like our fridge. when it is ferrie, it would rust
Atoms combine into domains or groups
When unmagnetized, the domains are random
When magnetized, the domains align in a common direction and the material becomes a magnet

70
Q

Magnetic field

A

The invisible lines of force surround a magnet. These are called flux lines

Flex lines
- Have polarity from North to South
- Always form a complete loop
- Do not cross each other
- Tend to form the smallest possible loop

71
Q

Permeability

A

The ability of a material to accept magnetic lines of force

If a magnets stick to it, it has a high level of permeability

72
Q

Electricity and Magnetism

A

A magnetic field is generated when current flows through a wire.

73
Q

Electronmagnets

A

Composed of many turns of wire close together
The principle of the electronmagnet
- When a wire is twisted into a loop
- The flux lines are brought together
- The flux lines are concentrated at the center of the loop
- A north and south pole are established
The strength of the magnetic field can be increased three ways
- The more turns of wire, the more flux lines are added together
- The greater the current, the greater the number of flux lines generated
- A ferromagnetic core is inserted into the center of the coil, usually iron

74
Q

Magnetic induction

A

The effect a magnet has on an object without physical contact

75
Q

Residual magnetism

A

The magnetic field that remains when an object is separated from a magnet.

76
Q

Retentivity

A

The ability of a material to retain its magnetic field after the magnetizing force is removed

77
Q

Magnetic shields

A

Low reluctance materials
Used to protect electronic equipment from magnetic flux lines

78
Q

Electromagnetic induction

A

The principle behind the generation of electricity
- A current is produced when a conductor passed or is passed by a magnetic field
- As the conductor passes through the magnetic field, a deficiency of electrons is created
- This results in a difference of potential between the ends of the conductor
- When the conductor is removed from the magnetic field, the free electrons return to their parent atoms.

79
Q

Faraday’s law

A

The induced voltage in a conductor is directly proportional to the rate at which the conductor CUTS the magnetic lines of force.

80
Q

The left hand rule

A

Thumb Motion
Index Flux (North to South)
Middle Current (Negative to positive)

81
Q

Magnetic and Electromagnetic Applications

A
  • AC generator: converts mechanical energy to electrical energy by utilizing the principle of electromagnetic induction.
  • DC generator: functions like an AC generator with the exception that it converts the AC voltage to DC voltage.
82
Q

Relay

A

An electromagnetic switch that opens and closes with an electromagnetic coil
- Used where it is desirable to have one circuit control another circuit
- it electrically isolates the two circuits
- Also used to control several circuits some distance away
- Doorbell

83
Q

Solenoid

A

A coil, when energized, pulls a plunger that does some mechanical work
- Door chimes
- Automotive starters

84
Q

Phonograph pickups

A

Used the electromagnetic principle
- A magnetic field is produced by a permanent magnet attached to the stylus
- The stylus tracks through the groove of a record in response to the audio signal recorded
- The movement induces a small voltage that varies at the audio signal response
- The induced voltage is amplified and used to drive a loudspeaker, rpoducing the audio signal

85
Q

Loudspeaker

A

Constructed of a moving coil around a permanent magnet
- The magnet produces a stationary magnetic field.
- The current passes through the coil, producing a magnetic field that varies at the rate of the audio signal
- The magnetic field of the coil is attracted and repelled by the field of the magnet
- The coil is attached to a cone that moves in response to the audio signal
- The cone reproduces the audio signal

86
Q

Magnetic recording

A

Uses the electromagnetic principle to store information
- A signal is stored on tape or disk with a record head, to be read back later with a playback head.
– Some are combined in one package
– They may be on the same head
- The record and playback heads are a coil of wire with a ferromagnetic core.
- A tiny gap between the ends of the core is a magnetic field
- A piece of material covered with iron oxide, is pulled across the record head, magnetizing it.
– Information is written in a magnetized pattern
- To play back or read the information, the material is moved past the gap in the playback head
- The magnetic field induces a small voltage into the coil winding
- When amplified, the information is reproduced.
Examples
- Floppy disk drives
- Hard disk drives
- Reel to reel recorders
- Cassette recorders
- Video recorder

87
Q

DC motor

A

Operation depends on the principle that a current-carrying conductor, placed in and at right angles to a magnetic field, tends to move at right angles to the direction of the field.

88
Q

TV, radar, computer terminals

A

Uses the current-carrying principle
- The conductor carrying current is deflected by a magnetic field
- The electrons travel through a vacuum to strike a phosphor screen where they emit light
- By varying the electron beam over the surface of the picture screen, a picture can be created.
- Two magnetic fields deflect the beam
– One field moves the beam from side to side
– One field moves the beam up and down

89
Q

Inductance

A

The characteristic of an electrical conductor that opposes a change in current flow

The symbol for inductance is L

Once current is moving through a conductor. Inductance helps to keep it moving

As the magnetic flux lines build up. They create opposition to the flow of current

Is measured by the henry
- Named after Joseph Henry
- Represented by H
- The amount of inductance required to induce an emf of 1 volt when the current in a conductor changes at the rate of 1 ampere per second
- Most commonly used are the millihenry (mH) and the microhenry(uH)

90
Q

Inductor

A

A device that stores energy in a magnetic field
Designed to have a specific inductance
Consist of a conductor coiled around a core
Classified by the type of core material, magnetic or nonmagnetic

When calculate inductance, it works just like resistance in series and parallel

91
Q

Lenz’s law

A

An induced emf in any circuit is always in a direction to oppose the effect that produced it. The amount of counter emf is in proportion to the rate of change. The faster the rate of change, the greater the counter emf

92
Q

Inductor - time constants

A

The time required for current through a conductor to increase to 63.2% or decrease to 36.8% of the maximum current

Expressed as t = L / R
t = time in seconds
L= Inductance in henries
R = Resistance in ohms

5 time constants required to fully build up or collapse the magnetic field of an inductor

93
Q

Types of inductors

A
  • Air core
  • Fernte or pawdered Ion core
  • Toroid core
  • Shielded core
  • Laminated core
94
Q

Capacitance

A

The ability of a device to store electrical energy in an electrostatic field

The letter C stands for capacitance

Similar to storage cells

The basic unit of capacitance is the farad (F)
A farad is the amount of capacitance that can store 1 coulomb (C) of charge when the capacitor is charged to 1 volt

95
Q

Capacitor

A

A device that possesses a specific amount of capacitance

Made of two conductors separated by an insulator
- The conductors are called plates
The insulators are called dielectric

Treat all capacitors as though they were charged
- Never touch both leads of a capacitor with your hands
- A capacitor can hold a potential indefinitely if it does not have a discharge path

Factors affecting capacitance
- Area of the plate
- Distance between the plates
- Type of dielectric material
- Temperature

96
Q

Dielectric constant

A

A measure of the effectiveness of a material as an insulator
Some examples
Paper: 2~3
Meca: 5~6

97
Q

Electrolytic capacitors

A

Large capacitance for size and weight
Consists of two metal foils separated by fine gauze saturated with a chemical paste called an electrolyte
Polarized, having a positive and negative lead

98
Q

How to calculate the capacitance

A

The opposite as resistance in series and parallel

99
Q

RC time constants

A

Reflects the time required for a capacitor to charge up to 63.2% of the applied voltage or to discharge down to 63.2%
t =RC
t = time in seconds
R = resistance in ohms
C = capacitance in farads

100
Q

Alternating Current (AC)

A

The father of AC is Nikola Tesla

101
Q

AC generator

A

Cycle: each time the AC generator completes on revolution, its output voltage is referred to as one cycle of output voltage. It produces one cycle of output current in a complete circuit
The two halves of a cycle are called alternations
Two complete alternations make up a cycle
One cycle per second is called a hertz (Hz)

102
Q

Armature

A

The rotating loop of wire

103
Q

AC values

A

Each point on a sine wave has two numbers associated with it
- The degree of rotation: the angle to which the armature has rotated
- The amplitude: The maximum departure of the value of an alternating current or wave from the average value

104
Q

Effective value

A

The amount that produces the same degree of heat in a given resistance as an equal amount of direct current

Can be determined by the root mean square (rms) process

Also called the rms value

Erms = 0.707E(peak)

105
Q

Period

A

The time required to complete one cycle of a sine wave

Measure in seconds

The letter t is used to represent period

106
Q

Frequency

A

The number of cycles that occur in a specific period of time
Expressed in terms of cycles per second
Unit of frequency is called hertz
One hertz equals one cycle per second

107
Q

Harmonics

A

Higher frequency sine waves that are exact multiples of the fundamental frequency (Represents the repetition rate of the waveform)

Odd harmonics are odd multiples of the FF, Even …

108
Q

AC Meters

A

Moving coil meter movement
- Referred to as D’Arsonval meter movement
- Designed to measure DC current
- AC current must be converted to DC current to be measured
- The process is called rectification
- The rectifiers covert the sine wave into a pulsating DC current

108
Q

Oscilloscopes

A

Most versatile piece of test equipment available for working on electronic equipment and circuits

Provide a visual display of what is occurring in the circuit

Oscilloscope provides
- The frequency of a signal
- The duration of a signal
- The phase relationship between signal waveforms
- The shape of a signal’s waveform
- The amplitude of a signal

The basic parts of an oscilloscope are
- A cathode ray tube (CRT)
- A sweep generator
- Horizontal and vertical deflection amplifiers
- Power supplies

109
Q

Resistive circuit

A

Just resistive load NO inductor and Capacitor

110
Q

Capacitive AC circuits

A

Capacitors in AC circuits
- AC voltage applied to a capacitor, gives the appearance that electrons are flowing in the circuit
- Current and voltage do not flow in phase with each other
– 90 degrees out of phase
– Current leads voltage

111
Q

Capacitive reactance/resistance

A

The opposition that capacitor offers to the applied AC voltage
Represented by Xc
Measured in ohms
Calculated by using the formula
Xc = 1 / 2π * fc
f stands for frequency
c stands capacitance

Can be used alone or combined with resistors to form RC (resistor-capacitor) networks

Used for filtering, phase shifting, coupling and decoupling

112
Q

A filter

A

A circuit that discriminates among frequencies, attenuating (weakening) some while allowing others to pass

Low pass filter and high pass filter

113
Q

Inductance in AC circuits

A

Inductors offer opposition to the current flow
- Voltage placed across an inductor creates a magnetic field
- When AC voltage changes polarity, it causes the magnetic field to expand and collapse.
- Voltage is induced in the inductor coil called a counter-electromotive force (CEMF)
– 180 degrees out of phase with the applied voltage
– Opposes the applied voltage
– Opposition is as effective in reducing current flow as a resistor
Voltage leading current, ELI, 90 degrees

114
Q

Inductive reactance

A

The opposition offered to current flow by an inductor
Measured in ohms
Depends on its inductance and the frequency of the applied voltage
Expressed by the symbol Xl
Xl=2π * fl
l = inductance in henries

115
Q

Applications of inductive circuits

A

Compete with capacitors for filtering and phase shift application
Have fewer applications than capacitors because they are larger, heavier and more expensive

116
Q

Inductor vs Capacitors

A

Inductors provide a reactive effect while still completing a DC circuit path
Capacitors provide a reactive effect, but block the DC elements
Inductors and capacitors are sometimes combined to improve the performance of a circuit
The effects of pure inductance or capacitance cause the voltage and current to be 90 degrees out of phase.
ELI (inductor) the ICE (capacitor) dude

117
Q

Cut off frequency

A

The frequency above or below the frequencies passed or attenuated is called the cut-off frequency
Symbol is fco
can be determined by the formula
fco = R / 2π * fL
L = inductance in Henries

118
Q

Reactance in Series Circuits

A

When an AC voltage source is applied, the instantaneous value of current flowing through the resistor varies with the alternating output voltage applied.

Ohm’s law applies

Peak current calculated from the source peak voltage

Rms current calculated from rms voltage

Voltage: Vt2 = Vr2 + Vl2
Resistance: Zt2 = R2 + Xl2
Power: Pappt2 = Pr2 (true power) + Pl2

119
Q

Impedance

A

The combined effect of resistance and reactance
Must be used to calculate current in a reactive circuit when the applied voltage is known
Represented by the symbol Z
The impedance of a parallel RL or RC circuit is smaller than both the individual resistance or reactance

120
Q

Reactance in parallel circuits

A

Parallel circuits containing inductors and capacitors maybe analyzed with vector diagrams
- Use current vectors
- Voltage across each component must be equal and in place

121
Q

Power consumption

A

In a purely resistive AC circuit
- Obtain the average power
– Calculate the product of the rms current and rms voltage

Power factor
- The ratio of true power in watts to apparent power in volt-amps

122
Q

Resonance

A

A resonance device produces a broadening and dampening effect
Resonant circuits pass desired frequencies and reject others
Occurs when a circuit’s inductive and capacitive reactance are balanced Xl = Xc

Resonant circuit
- Both inductive and capacitive components at the same frequency
– Reactances are equal but opposite
- Used with radio frequencies in tuning receivers and transmitters
- Not used in the audio bands of frequencies

123
Q

Transformer

A

The action caused when two electrically isolated coils are placed next to each other and an AC voltage is put across one coil. Resulting in a changing magnetic field which induces a voltage into the second coil.

The device used to create this action is called a transformer

The coil containing the AC voltage is the primary winding. The coil in which the voltage is induced is the secondary winding

The design of a transformer is determined by
- The frequency at which it will be used
– Low -frequency, iron cores
– High frequency, air cores
- The power it must handle
- The voltage it must handle

Transformers are rated in volt-amperes

Transformers are wound with tapped secondaries
- Center tapped secondary is equal to two secondary windings
- Used for power supply to convert AC voltages to DC voltages.

124
Q

Coefficient of coupling

A

A number from 0 to 1

The coupling coefficient is defined as the fraction of the magnetic flux produced by the current in one coil that links with the current in the other coil.

125
Q

Turns ratios

A

Determines whether a transformer is used to step up (greater than one), step down (less than one) or pass voltage unchanged (Isolated transformer)

The number turns in the secondary winding divided by the number of turns in the primary winding

Expressed as turns ratio = Nsec / Nprim
Where N = number of turns

Either step up or step down, power is the same.

Impedance ratio is equal to the turns ratio squared
- Zp / Zs = Np2 / Ns2

126
Q

Semiconductor materials

A

Three pure semiconductor elements
- Carbon C
- Germanium Ge
- Silicon Si most commonly used

127
Q

Covalent bonding

A

The process of sharing valence electrons, resulting in the formation of crystals

128
Q

Negative temperature coefficient

A

As the temperature increases, its resistance decreases

For silicon, resistance cuts in half every 60 C rise in temperature

129
Q

Hole

A

The absence of an electron
Represents the loss of a negative charge
Therefore, it has the characteristics of a positively charged particle
Each corresponding electron and hole are referred to as an electron-hole pair
Holes constantly drift toward the negative terminal of the voltage source.
Electrons flow toward the positive terminal
Current flow in a semiconductor consists of the movement of both electrons and holes
The amount of current flow is determined by the number of electron-hole pairs

130
Q

Doping for semiconductors

A

A process to increase conductivity
Doping is the process of adding impurities to a semiconductor material
- Pentavalent, atoms with five valence electrons
– N-type material
— Has more electrons than holes
— Negative charge is the majority carrier
— Free electrons flow toward the positive terminal
- Trivalent, atoms with three valence electrons
– P-type material
– Has more holes than electrons
— Positive charge is the majority carrier
— The holes move toward the negative terminal
Diodes, created by joining N and P-type materials together

131
Q

PN Junction Diodes

A

Junction diodes are created by joining N-type and P-type materials together
The depletion region is the area near the junction
The charge at the junction creates a voltage called a voltage barrier
Current flows through a diode only when the external voltage is greater than the barrier voltage
A diode that is forward-biased conducts current
A diode that is reverse-biased conducts only a small leakage current
A diode is a one-directional device
The arrow on a diagram means the flow of holes
P-Type is called Anode
N-type is called Cathode

132
Q

Transistor construction

A

A bipolar transistor is produced when a third layer is added to a semiconductor
It can amplify power, current or voltage
Also called a junction transistor or transistor
Can be constructed of germanium or silicon (more popular)
Consists of three alternately doped regions
The regions are arranged two ways
- P-type material is sandwiched between two N-type materials NPN transistor
- N-type material is sandwiched between two P-type materials PNP transistor
It has three points, emitter, base and collector

current flows 100% in emitter and 99% in collector

Transistors are identified by a number
- Begin with 2N and up to four more digits
- Identify the device as a transistor
- indicate that it has two junctions

The basic functions of a transistor are
- to provide current amplification of a signal
- to switch a signal

A transistor must be properly biased
- The emitter junction is forward-biased
- The collector junction is reverse-biased

133
Q

Junction field effect transistors (JFETs)

A

A unipolar transistor that functions using only majority carriers
Voltage operated
Constructed from N-type and P-type semiconductor materials
Capable of amplifying electronic signals
JFETs have three electrical connections
- One lead is connected to the substrate to form the gate (G)
- One lead is connected to each end of the channel to form the source (S) and the drain (D)

JFET requires external 2-bias voltages to operate
- One is connected between the source and the drain, forcing the current to flow through the channel
- One is connected between the gate and the source, controlling the amount of current flowing through the channel

The side of the depletion region is controlled by the voltage gate-source
- As the voltage increases, so does the depletion region
- As the depletion region increases, the size of the channel is reduced, thus reduces the amount of current flow and can be used to control drain flow

The amount of gate to source voltage required to reduced the drain current to zero is the gate to source cut off voltage

The drain to source voltage has control over the depletion region within the JFET
- As the voltage increases, so does the current
- A point is reached where current levels off, even though voltage still increases
- The value of the drain source voltage required to pinch off or limit the drain current is called pinch off voltage

134
Q

Metal oxide semiconductor field effect transistors (MOSFETS)

A

Do not use PN junction
Use a metal gate
- electronically isolated from the semiconductor channel by a thin layer of oxide
- Two important types of MOSFETs
– N-type units with N channels
— Called depletion mode devices
— They conduct when zero bias is applied
– P-type units with N channels
— Called enhancement mode devices
— Electron flow is cut off until it is aided or enhanced by the bias voltage on the gate

135
Q

Silicon controlled rectifiers (SCR) AKA Thyristors

A

Three terminals
- anode
- cathode
- gate
Used primarily as switches
Controls current in only one direction

A power transistor would require ten times the trigger signal of an SCR to control the same amount of current

Constructed of four alternately doped semiconductor layers
- Three junctions are formed

A small gate current can control a large load current

136
Q

Amplifier

A

Electronic circuits used to increase the amplitude of an electronic circuit
Amplifier configuration
- The transistor can be connected in 3 different circuit configurations
– The common base circuit
– The common emitter circuit
– The common collector circuit
- One lead serves as a common reference point and the other two leads serve as input and output connections
- Each configuration can be constructed using NPN or PNP transistors
- The transister’s emitter base junction is forward biased
- The collector base junction is reverse biased
- The common emitter circuit is the most widely used, 180 degree phase shift

Electronics (1 decks)

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