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Electrician Apprentice Year 1 Canada > BWC 131 - Extra Low Voltage, Magnetism and Meters > Flashcards

BWC 131 - Extra Low Voltage, Magnetism and Meters Flashcards

1
Q

What are the elastic lines that make up the magnetic field

A

Lines of Flux

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2
Q

The ability for a material to carry a magnetic field is called

A

Permeability

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3
Q

The inverse effect of permeability is called

A

Reluctance

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4
Q

How do Lines of Flux behave

A

Exit the north pole re-enter the south pole.

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5
Q

Like Poles

A

repel

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6
Q

unlike poles

A

attract

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7
Q

What is Flux Density

A

Measure of Field Concentration

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8
Q

What is the driving force for all magnetic Fields

A

Magneto motive force (mmf

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9
Q

Where is the Magnetic field the strongest

A

close to the conductor

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10
Q

If two conductors are in parallel and current is in the same direction what happens to the conductor

A

the are drawn together

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11
Q

If two conductors are in parallel and current is in different direction what happens to the conductor

A

The are pushed apart

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12
Q

What is a newton

A

Force of Gravity

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13
Q

When a conductor is wound into a coil the magneto-motive force that surrounds the conductor becomes

A

much more concentrated

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14
Q

What type of core do most magnets have?

A

Iron

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15
Q

What is a core made of

A

Air or Iron

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16
Q

breaks in a magnetic circuit are dalled

A

air gaps

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17
Q

what is the function for magnetic strength

A

size of the poles and flux density

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18
Q

how do magnetic fileds flow

A

they expand or contract in concentric loops

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19
Q

what is it called when the reluctance of the core is infinite and
the field through the core of the electromagnet will not increase regardless of the increase in the current through the coil.

A

saturation

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20
Q

the way a response lags behind its cause is

A

Hysteresis

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21
Q

how well a magnetic material retains its magnetism after the
magnetizing force is removed is called

A

Retentivity

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22
Q

the magnetic material retained after the
magnetizing force is removed is called

A

Residual Magnetism

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23
Q

the magnetizing force it takes to reduce the residual magnetism to zero

A

coercive force

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24
Q

a localized electric current induced in a conductor by a varying magnetic field is called

A

eddy currents

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25
Q

A ________ contains one or more contacts that are operated electromagnetically.

A

relay

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26
Q

When there is a change in the amount of magnetic flux linked by a circuit, an electromotive force (emf) is induced into that circuit. The magnitude of the emf is proportional to the rate at which the flux is changing is whos law

A

Faraday

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27
Q

the direction (polarity) of the induced emf will be such that the
magnetic effect of any current resulting from that emf will oppose the
change in flux that produced it is whos law

A

Lenz

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28
Q

The ____________ consists of several turns of fine copper wire wound on an aluminum frame.

A

Moving Coil

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29
Q

The two methods used to damping a moving-coil meter are

A

air damping and eddy current damping

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30
Q

meter scales are not always

A

Linear

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31
Q

what is he apparent shift in an object’s position as it is viewed from different angles.

A

parallax error

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32
Q

________ are misleading voltage readings that are caused by such things as stray induction, capacitive coupling, and insulation leakage

A

Ghost readings

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33
Q

What do the Letters “OL” stand for on a meter

A

Over Range

34
Q

Where do the black leads go on a meter

A

COM

35
Q

Where do red leads go on a meter

A

V/Ohms

36
Q

the voltage range can be increased dramatically by adding a _________ to the meter circuit.

A

Multiplier resistor

37
Q

The Ω/V rating found on analog meters is referred to as the meter’s

A

Sensitivity

38
Q

The intensity of a magnetic field is called

A

Flux Density

39
Q

A ________ is surrounded by an invisible magnetic field.

A

Permanent Magnet

40
Q

What is the driving force for all magnetic fields

A

Magnetomotive Force

41
Q

If current flows in the same direction the fields will ________ and be drawn together

A

Combine

42
Q

if current flows in opposite directions fields will become _________ forcing conductors apart

A

compressed

43
Q

winding conductors into a coil creates a ?

A

Electromagnet

44
Q

which three factors determine strength of the magnetic field

A
  • Current Flow
  • number of coil wraps
  • core material
45
Q

what is potential difference

A

Voltage

46
Q

How is a shunt connected?

A

in parallel

47
Q

a typical shunt has very low ________

A

resistance

48
Q

why are shunts made of material with low temp coefficients

A

min resistance change

49
Q

why is it important to have a shunt with low resistance `

A

doesn’t change normal circuit

50
Q

never connect/disconnect a ammeter from the circuit when its ________

A

energized

51
Q

what does the term meter loading mean?

A

when a meter alters the current flow

52
Q

under what conditions does meter loading become a problem

A

when the meter has a higher resistance then the circuit

53
Q

shunts reduce high current to _________

A

Milivolt Outputs

54
Q

what does Instrument is used for measuring very low levels of resistance

A

Wheatstone bridge

55
Q

what test is used to determine if a circuit/ device is continuous.

A

Continuity test

56
Q

to find the resistance of a single component, the component must first be _____

A

isolated

57
Q

Never assume that a failed circuit has been ________

A

De-energized

58
Q

why is it important to keep fingers off the probes when measuring resistance

A

you will measure resistance of body and circuit

59
Q

with the probes shorted together you can

A

zero the meter

60
Q

An analog meter should be ________ before each use

A

zeroed

61
Q

An analog Ohm meter moves _______ proportional to the current

A

Inversely

62
Q

Typical ranges for an analog meter are

A

Rx1
Rx100
Rx10,000

63
Q

For max accuracy bring the pointer to the _______ of the scale

A

Right side

64
Q

An OL on a meter means

A

Over Range

65
Q

0 Ohms in a meter means that _____

A

The meter is incapable of measuring the resistance as its to low

66
Q

typical meter leads have a resistance of

A

0.2-0.4 Ohm

67
Q

__________ are charge storage devices

A

Capacitors

68
Q

A Capacitor must be __________ before testing

A

Discharged

69
Q

When voltage in a capacitor are equal to that in the battery what happens the the current.

A

Current will stop

70
Q

Diodes are electrical Equivalent of a

A

Check Valve

71
Q

When a Diode fails it becomes

A

Open / Short

72
Q

Functional Diodes may test @

A

Several Kilohms

73
Q

What are the 7 Ohmeter Precautions and Procedures

A
  1. Make sure the circuit/component are De-energized
  2. Make sure the circuit/components are isolated from the capacitor
  3. Zero out the analog meter
  4. For Digital meters measure the initial lead resistance.
  5. completely isolate the component to be tested.
  6. Don’t touch the tips of the probes while testing.
  7. Don’t leave the meter on ohms when finished
74
Q

What makes up a Wheastone Bridge

A
  • Battery
  • Zero Center Galvanometer
  • Three adjustable precision resistors
75
Q

Two resistors on a Wheatstone Bridge are called

A

Ratio Arms

76
Q

Ratio Arms have precise multiples of

A

1:1000 to 1000:1

77
Q

The Third resistor of a Wheastone Bridge is controlled by

A

4 individual switches

78
Q

What is the Equation used to calculate resistance of a Wheatstone Bridge

A

(R1/R(Rx/R3)

79
Q

Magohm Meter provide a DC Test Voltage from _________

A

100V - 5000V

80
Q

What are precautions using a Megohm Meter

A
  • Don’t Connect to a energized circuit
  • They have there own internal power supply
  • Don’t make contact with Megohm meter leads during operation
  • don’t use to test low voltage
  • discharge the equipment before considering it safe to touch.
81
Q

The electrons that leak through insulation to ground or to other conductors is ________

A

Leakage Current

Electrician Apprentice Year 1 Canada (1 decks)

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