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Physics 101-2 (metc) > Lesson 1 > Flashcards

Lesson 1 Flashcards

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1
Q

Electrostatics

A

The study of stationary or resting electric charges

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2
Q

Ground

A

A connection made to the earth, ground potential is 0

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3
Q

Electrification

A

Process where electrons are added or removed from a body

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4
Q

Friction

A

The simplest and most fundamental means of electrification. Involves the transfer of electrons from one object to another by rubbing.

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5
Q

Repulsion - attraction

A

Like charges repel , unlike charges attract

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6
Q

The inverse square law is also known as

A

“Columbs law of electrostatics”

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7
Q

When there’s friction, the object gaining electrons becomes ________ charged, b/c of the imbalance between _______ and ________. The object loosing electrons becomes _____ charged.

A

negatively , protons , neutrons , positively

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8
Q

What is an example of friction ?

A

wool (- charge) + balloon (+ charge)

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9
Q

Contact

A

happens when 2 objects touch to allow flow of electrons

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10
Q

Induction

A

electrical fields responding to each other by being in each others vicinity without the objects actually touching.

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11
Q

Electrons of a _______ body are attracted by the positive charge or repulsed by the negative charge of the charged body.

A

neutral

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12
Q

What are the 5 parts to the laws of electrostatics?

A 
repulsion-attraction
the inverse square law 
distribution
movement 
concentration
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13
Q

inverse square law

A

the force between two charges is directly proportional to the product of their magnitude and inversely proportional to the squared distance between them

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14
Q

inverse square law formula

A 
2
I           D
  1           2
\_\_\_\_=\_\_\_\_\_
               2
I            D
   2           1
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15
Q

Distribution

A

the result of the repulsion-attraction law as electrons try to repel

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16
Q

Distribution: Charges are on the ______ _______ of conductors.

A

external surfaces

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17
Q

Movement: only ________ move along the solid conductors. _______ are tightly bound inside the _______ ________ which do not drift in solid conductors.

A

electrons , protons , atomic nuclei

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18
Q

Concentration: the greatest concentration of charge will be on the surface where the _______ is greatest.

A

curvature

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19
Q

Static discharge

Occurs with a difference in charges becoming ____ an the distance ______. The static discharge release excess ______ in the form of ______ _______ and sound.

A

2 oppositely charged objects are close and the electrons jump the gap for equalization of charges.

big , small , light photons

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20
Q

Electrodynamics

A

the study of electric charges in motion

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21
Q

Potential Difference

A

the force or strength of electron flow

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22
Q

Potential difference is also called ?

A

Electron Motive Force (EMF)

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23
Q

Electron Motive Force (EMF)

A

max difference of potential between + and - ends

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24
Q

The greater electrons at a point and the deficiency of electrons at another the greater attraction or _______ between the points.

A

potential

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25
Q

What is the unit of measure for potential difference?

A

volt

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26
Q

current

A

the flow of electrons through a conductor

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27
Q

conductor

A

any thing where electrons can flow easily

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28
Q

What is current measured in?

A

amperes

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29
Q

Intensity of electric current is found by?

A

the # of electrons flowing past a point in 1 second

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30
Q

Current consist of the movement of _______ electrons per second.

A

6.24 x 10^18

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31
Q

What are the types of current ?

A

direct and alternating

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32
Q

Direct Current

A

electrons flow in the same direction through a conductor

*** pulsating

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33
Q

A battery produces ______ ______ ; electrons move from the repelling negative terminal and toward the attracting positive terminal, always moving through the circuit in the _____ ______.

A

direct current , same direction

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34
Q

Alternating Current

A

electrons move first in direction and then reverse move in the other direction through a conductor

***oscillating

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35
Q

Resistance

A

the amount of opposition to the flow of electrons in an electric circuit

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36
Q

What is the unit of measurement for resistance

A

ohms represented by the omega symbol

37
Q

The _____ is defined as the resistance to a flow of current offered by a column of mercury 106.3 cm long with a diameter of 1 square millimeter at 0 degrees Celsius.

A

ohm

38
Q

Resistance is dependent on ?

A

type, physical dimensions, and temperature of material

39
Q

Resistance:
type of material

The valence electrons of metal atoms are very ____ bound and can be easily _______ to move through the material.

________ is used in electric wiring more often than any other metal as it offers less resistance to the flow of electric current compared to other common material. It material is tightly bound.

A

loosely , detached

copper

40
Q

Resistance:

physical dimensions of the material

A

length
(longer the wire , greater the resistance )

thickness/ diameter
(thicker the wire , less the resistance )

41
Q

Resistance:

Temperature of the material

A

resistance decreases as the temperature is decreases

***electric current is then increased

42
Q

Electrical Circuit

A

a pathway usually made of copper that allows electrons to move in a complete circle from its source going through devices and then back to the source.

43
Q

What are the 3 requirements for an electrical circuit?

A

voltage , conductor , and resistance

44
Q

Most application require this type of electric current…

A

alternating current

45
Q

What is the graph of waveform for a direct current ?

A

straight line (voltage all positive)

46
Q

What is the graph of waveform for a alternating current?

A

sine curve (voltage initial positive up to a peak, then returns to 0 momentarily, to negative peak next, then back to 0.)

47
Q

Simple/Electric Generator or Dynamo

A

its made of a conductor and magnets and it converts mechanical energy to electrical energy with moving flux lines that induce a current

48
Q

what are the components of an electric generator?

A

magnets, armature (conductor) , slip ring , stationary brushes

49
Q

magnets

A

the source of magnetic fields

50
Q

armature (conductor)

A

coil of wire between magnetic poles used to encounter the strongest lines of force

51
Q

slip ring

A

2 metallic rings isolated and they rotate with the armature

52
Q

stationary brushes

A

metal strips that conduct current from the armature to be transmitted to the external circuit

53
Q

What fingers go with what in Flemings right hand generator / dynamo rule?

A

thumb = motion of conductor
index = magnetic field / flux
middle finger = current

54
Q

Summarize the actions of a simple generator.

A

An armatures motion is parallel to the lines of force. As the armature rotates the voltage/current goes upward to a peak of EMF at 90 degrees from a starting point at 0 degrees. There is more and more cutting of flux lines. The armature continues to turn and the angle decreases along with less and less cutting of flux lines. The induced voltage returns to zero. (90-180 degrees) Following this the voltage/current increases/is induced to a downward peak at 270 degrees. Flux lines then start to be cut more and more and the current returns to 0 at 360 degrees.

55
Q

what is the unit of measure for a generators frequency in the united states?

A

hertz

56
Q

American and Canadian generators operate at how many cycles per second (cps)?

A

60

57
Q

The frequency of the sine wave from the cycles per second in a generator is found by what?

A

1cps=1hz

58
Q

Describe the sine wave seen in a generator.

A

1 positive and 1 negative cycle (2 alterations split in half)

59
Q

Single Sine Curve
Represents a ______ ______ ___ _____

Average value = ___ of the amplitude. The average of a half cycle is equal to ______ times the peak value. _______ or the peak value is the _______ value of a given alternation measured from zero to peak. ______ used in radiography is expressed in peak values.

A

single phase of AC

63.7% , 0.637 , peak value , amplitude , maximum, kilovoltage

60
Q

Voltage Ripple

The ____ _____ made during a full-wave rectification.

The fluctuation of current and voltage is expressed by a “_____ _____”

Voltage is not constant therefore _____ ____ _______ ______ _____ ______.

A

net voltage

sine wave

pulsating DC produces a ripple effect

61
Q

AC Generator (polyphase)

A

no commutator is used, this cause the voltage (emf) to vary from a positive value to an equal but negative value

62
Q

AC Generator (polyphase)

For two-phase generators, the two armatures are ____ degrees out of phase.

For three-phase generators (most commonly used in _______ _______) the three armatures are _______ degrees out of phase.

A

90 , x-ray circuits, 120

63
Q

DC Generator

A

uses a commutator and the voltage (emf) varies from 0 to a maximum positive value.

64
Q

DC Generators

A _______ is a slip ring cut in half with each connected to one end of an armature wire.

The gap in both sides of the commutator ring causes the direct current to stop for a brief moment. The creates _____ ______ _______.

A

commutator , pulsating direct current

65
Q

What are the advantages of using an AC generator over a DC?

A

transformers use an alternating current for the changing magnetic field that induces voltage in the secondary coil.

Theres also less power loss in AC.

66
Q

What is meant by AC having less power lost?

A

this refers to the ability to step up voltage and step down current during transmission.

67
Q

Transformer

A

transforms electric current into higher or lower intensities

68
Q

What are the names for the transformer coils?

A

primary and secondary

69
Q

Transformer Primary Coil

A

connected to the source supplies (where the volts enter) w/ the alternating current

70
Q

The transformer primary coil is on what side?

A

input

71
Q

Transformer secondary coil

A

develops AC by mutual induction

72
Q

The transformer secondary coil is on what side?

A

output

73
Q

Step-up transformer

A

when the voltage is increased from the primary to the secondary (the primary coil has less wraps around)

74
Q

Step-down transformer

A

when the voltage is decreased from the primary to the secondary (the primary coil has more wraps around)

75
Q

What are the construction types of transformers using the primary and secondary coils?

A

air core , open core, closed core, shell-type

76
Q

Air Core

A

2 coils of wire in proximity to facilitate induction

77
Q

Open Core Transformer

A

coils filled with an iron core, strength of the magnetic field increases induction

78
Q

Closed Core Transformer

A

closing the core directs the lines of force from the primary to the secondary coils toward each other and result in an increase in field strength (half a center block with coils on both sides)

79
Q

What type of generator uses a shell-type transformer?

A

x-ray

80
Q

shell-type transformer

A

converges the inside and outside lines of force through an iron core

both coils are wound around the center of core of like a center block with 2 open squares

81
Q

Transformer Efficiency

A

ability of a transformer to avoid power loss

82
Q

What are the types of power loss in a transformer?

A

I^2R , eddy current, hysteresis (lagging)

83
Q

I^2R is sometimes called what? and what does I and R stand for?

A

“copper loss” , current and resistance

84
Q

What can reduce the cause of I^2R loss?

A

a large diameter copper wire

85
Q

Eddy current power loss

A

result of currents making heat in the core and opposing the cause that made them according to lenz’s law

86
Q

Hysteresis Power loss is alos known as?

A

lagging loss

87
Q

What can be done to prevent eddy current power loss?

A

laminating the transformer core to reduces eddy current into thin layers

88
Q

What can be done to prevent hysteresis power loss?

A

laminated silicon iron core

89
Q

Hysteresis loss (lagging loss)

A

happens when energy is expended along with changing AC magnetimizing the core material. The reorientation of the magnetic dipoles needs energy and makes heat in the core which waste electrical power.

Physics 101-2 (metc) (3 decks)

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