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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
What is the unit of measure for potential difference?
volt
26
current
the flow of electrons through a conductor
27
conductor
any thing where electrons can flow easily
28
What is current measured in?
amperes
29
Intensity of electric current is found by?
the # of electrons flowing past a point in 1 second
30
Current consist of the movement of _______ electrons per second.
6.24 x 10^18
31
What are the types of current ?
direct and alternating
32
Direct Current
electrons flow in the same direction through a conductor *** pulsating
33
A battery produces ______ ______ ; electrons move from the repelling negative terminal and toward the attracting positive terminal, always moving through the circuit in the _____ ______.
direct current , same direction
34
Alternating Current
electrons move first in direction and then reverse move in the other direction through a conductor ***oscillating
35
Resistance
the amount of opposition to the flow of electrons in an electric circuit
36
What is the unit of measurement for resistance
ohms represented by the omega symbol
37
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.
ohm
38
Resistance is dependent on ?
type, physical dimensions, and temperature of material
39
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.
loosely , detached copper
40
Resistance: | physical dimensions of the material
length (longer the wire , greater the resistance ) thickness/ diameter (thicker the wire , less the resistance )
41
Resistance: | Temperature of the material
resistance decreases as the temperature is decreases ***electric current is then increased
42
Electrical Circuit
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
What are the 3 requirements for an electrical circuit?
voltage , conductor , and resistance
44
Most application require this type of electric current...
alternating current
45
What is the graph of waveform for a direct current ?
straight line (voltage all positive)
46
What is the graph of waveform for a alternating current?
sine curve (voltage initial positive up to a peak, then returns to 0 momentarily, to negative peak next, then back to 0.)
47
Simple/Electric Generator or Dynamo
its made of a conductor and magnets and it converts mechanical energy to electrical energy with moving flux lines that induce a current
48
what are the components of an electric generator?
magnets, armature (conductor) , slip ring , stationary brushes
49
magnets
the source of magnetic fields
50
armature (conductor)
coil of wire between magnetic poles used to encounter the strongest lines of force
51
slip ring
2 metallic rings isolated and they rotate with the armature
52
stationary brushes
metal strips that conduct current from the armature to be transmitted to the external circuit
53
What fingers go with what in Flemings right hand generator / dynamo rule?
thumb = motion of conductor index = magnetic field / flux middle finger = current
54
Summarize the actions of a simple generator.
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
what is the unit of measure for a generators frequency in the united states?
hertz
56
American and Canadian generators operate at how many cycles per second (cps)?
60
57
The frequency of the sine wave from the cycles per second in a generator is found by what?
1cps=1hz
58
Describe the sine wave seen in a generator.
1 positive and 1 negative cycle (2 alterations split in half)
59
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.
single phase of AC 63.7% , 0.637 , peak value , amplitude , maximum, kilovoltage
60
Voltage Ripple The ____ _____ made during a full-wave rectification. The fluctuation of current and voltage is expressed by a "_____ _____" Voltage is not constant therefore _____ ____ _______ ______ _____ ______.
net voltage sine wave pulsating DC produces a ripple effect
61
AC Generator (polyphase)
no commutator is used, this cause the voltage (emf) to vary from a positive value to an equal but negative value
62
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.
90 , x-ray circuits, 120
63
DC Generator
uses a commutator and the voltage (emf) varies from 0 to a maximum positive value.
64
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 _____ ______ _______.
commutator , pulsating direct current
65
What are the advantages of using an AC generator over a DC?
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
What is meant by AC having less power lost?
this refers to the ability to step up voltage and step down current during transmission.
67
Transformer
transforms electric current into higher or lower intensities
68
What are the names for the transformer coils?
primary and secondary
69
Transformer Primary Coil
connected to the source supplies (where the volts enter) w/ the alternating current
70
The transformer primary coil is on what side?
input
71
Transformer secondary coil
develops AC by mutual induction
72
The transformer secondary coil is on what side?
output
73
Step-up transformer
when the voltage is increased from the primary to the secondary (the primary coil has less wraps around)
74
Step-down transformer
when the voltage is decreased from the primary to the secondary (the primary coil has more wraps around)
75
What are the construction types of transformers using the primary and secondary coils?
air core , open core, closed core, shell-type
76
Air Core
2 coils of wire in proximity to facilitate induction
77
Open Core Transformer
coils filled with an iron core, strength of the magnetic field increases induction
78
Closed Core Transformer
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
What type of generator uses a shell-type transformer?
x-ray
80
shell-type transformer
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
Transformer Efficiency
ability of a transformer to avoid power loss
82
What are the types of power loss in a transformer?
I^2R , eddy current, hysteresis (lagging)
83
I^2R is sometimes called what? and what does I and R stand for?
"copper loss" , current and resistance
84
What can reduce the cause of I^2R loss?
a large diameter copper wire
85
Eddy current power loss
result of currents making heat in the core and opposing the cause that made them according to lenz's law
86
Hysteresis Power loss is alos known as?
lagging loss
87
What can be done to prevent eddy current power loss?
laminating the transformer core to reduces eddy current into thin layers
88
What can be done to prevent hysteresis power loss?
laminated silicon iron core
89
Hysteresis loss (lagging loss)
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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