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Construction Electrician Level 2 > Study Test Questions D1 > Flashcards

Study Test Questions D1 Flashcards

1
Q

If the peak to peak voltage is 588.4 and the heating load is 2000watts of heat what is the resistance of this heat?

A

Peak to peak voltage / 2 =
peak voltage x 0.707 = E (RMS)

R= E*2/P

588.4/2= 294.2Em x 0.707= 208E

208*2\2000=21.632 ohms

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2
Q

If a source has an instantaneous voltage of 50 at 18• degrees, what would the instantaneous voltage be at 80degrees?

A

Instant to peak voltage
50E x sine 18• = 161.8Em

First angles max voltage to another angle at max voltage.

161.8Em x 80• = 159.34Em

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3
Q

State three reasons why alternating current is used more than direct current?

A

Cheaper, smaller, simpler, the step up or step down fiction of a transformer

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4
Q

List five applications where direct current is preferred or required instead of alternating current.

A

Mining, high intensity light sources that use carbon arcs, electro-plating, battery charging, precise speed, synchronized motors and alternators

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5
Q

What does Epp stand for?

A

Peak to peak value

2 X the peak

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6
Q

What is another name for RMS OR ROOT MEAN SQUARE?

A

Effective Value

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7
Q

At what angle in a sine wave does peak value occur?

A

90° and -270°

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8
Q

With respects to the peak value, what is the average value of an AC sine wave?

A

0°

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9
Q

With respects to the peak value, what is the average value of one alternation of an AC Sine wave?

A

.637

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10
Q

What two meters must be use to determine the effective resistance of an AC circuit?

A

Watt meter and amp meter

Ohm and volt meters might explode

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11
Q

What term is used to refer to the circulating currents in a magnetic core?

A

Eddy currents

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12
Q

As the frequency of the AC Increases, the effective resistance_____________.

A

Increases

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13
Q

What are the three formulas for finding Frequency, voltage and number of field poles?

A

F= PxN/120

N= 120xF/P

P= 120xF/N

P= poles
N= speed in rpm
F= Frequency
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14
Q

The peak power in an AC lighting circuit is 1200w. What is the effective power in that circuit?

A

P= 0.5 x Pm

= 0.5x1200w

=600w

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15
Q

What is the instantaneous voltage at 30° into the AC cycle on a sine wave with an effective value of 480E?

A

E= 0.707x Em

Em= E/0.707

= 480/0.707x VOLTAGE
=679 Em
e = sine 30°x 679V
=0.5x 679v

= 339.5e

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16
Q

If an AC source with a peak voltage of 339.4 Em is placed across a load with a resistance of 288ohms, what power will the resistance dissipate?

A

E= 0.707 x Em

P= E*2/R

200w

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17
Q

What is the frequency of an alternating voltage produced by a 10-pole alternator turning at a speed of 600rpm?

A

F= PxN/120

50hz

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18
Q

An turns at a speed of 450 rpm and produces an alternating current of 60 Hz. How many poles does this alternator contain?

A

P= fx120/ N

16 poles

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19
Q

At what rpm must a prime mover turn a six pole alternator to produce an alternating voltage with a frequency of 50Hz?

A

N= 120xF/P

1000rpm

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20
Q

What is the effective voltage of a sine wave with a peak value of 679 volts?

A

E = Em x 0.707

480.053 E

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21
Q

What is the average value of one alternation of a sine wave with an effective value of 277 volts?

A

Eav= 277

Eav/0.707= Em

Em x .631= E

247.22

22
Q

What three quantities affect the magnitude of an induced Emf?

A

Active length, Flux density, velocity

23
Q

In Flemings left hand rule which direction does the middle finger point?

A

Direction of induced electron current flow,

Index= direction of field

Thumb= thrust or motion of conductor

24
Q

What is meant by electromagnetic term “prime mover”?

A

The device supplying energy to the generator.

25
Q

A conductor has an active length of 2meters. To induce a voltage of 240 volts, at what velocity must it be pushed through a field of flux density 1.1T (tesla)

A

V=e/BL

109 m/s

26
Q

A conductor is to be pushed through a field with a flux density of 1.5Tesla at a velocity of 100 m/a to produce a voltage of 347v. What must the active length of the conductor be?

A

L= e/BV

2.3m

27
Q

To increase the field flux density in a generator, would the resistance of the field rheostat have to be increased or decreased?

A

Decreased

28
Q

The unit of inductance is the

A

L for Henry

29
Q

Increasing the length of the magnetic circuit in an inductor ________ it’s inductance

A

Decreases

30
Q

Adding a ferrite core to a coil will cause it’s inductance to ______

A

Increase

31
Q

State the equation that relates induced voltages to inductance

A

E = -L x(^I/^t)

32
Q

What does the abbreviation cemf stand for?

A

Counter electromagnetic force

33
Q

When a conductor is cut by two webers of flux lines in one second, what is the induced voltage?

A

2 volts

34
Q

Tripling the number of turns in an inductor increases the inductance _________ times.

A

Nine

35
Q

Calculate the total equivalent capacitance in a circuit consisting of four capacitors with the following values connected in series:
20uF, 30uF, 50uF, 60uF?

A

(1/.00002)+(1/.00003)+(1/.00005)+(1/.00006)=.00000833(8.33uF)

36
Q

What would the total equivalent capacitance be for the following four capacitors connected in parallel?
5uF, 10uF? 20uF, 60uF

A

95uF
Add all the sums together.

series you add as followed 1/Ft= 1/Fa+1/Fb+1/Fc

37
Q

When a capacitor is discharging from a fully charged state, what percentage of the source voltage will exist across the capacitor after one time constant?

A
  1. 3%

63. 7-100=36.3

38
Q

Define capacitance?

A

Capacitance is the property if an electric circuit which opposes any change in voltage across the circuit

39
Q

As voltage across the capacitor increases, the current flowing through the circuit _______ and the voltage across the current limiting resistor ______.

A

Decreases, decreases

40
Q

What is the formulas for calculating time constants of a circuit in terms of its capacitance and resistance?

A

T= RC

41
Q

Where does the capacitor store it’s energy?

A

The capacitor stores it’s energy in the electric field between it’s played and in the distortion of the orbitals in its dielectric.

42
Q

What equation that determines maximum current in an RC circuit?

A

I = Es/R

43
Q

What is the equation for one coulomb?

A
  1. 24 x 10*18=1 coulomb

* = power

44
Q

What is the formula for Coulomb’s law of electrostatic force?

A

F= k Q1xQ2/d*2

F= the force of attraction or repulsion between charges in newtons.

K= the constant of proportionality for the type of medium between the two charges.

Q= the magnitude of the charges in coulombs.

d = the distance between the charges in the metres. P

*= power

45
Q

The forces between two points of electric charges is______ proportional to the square of the distance between them, and ______ proportional to the product of the two charges

A

Inversely , directly

This is coulombs electrostatic field law

46
Q

What is a dielectric?

A

A dielectric is an insulator exposed to an electric field.

47
Q

What is the unit of electric field intensity?

A

An electric field may be expressed in either Volts per meter or newtons per coulomb.

48
Q

State the formula for calculating the capacitance of a capacitor.

A

C= 8.85 x 10*-12 x Kx A/d

*= power

49
Q

Name two devices that can be used to discharged a built up charge safely.

A

Field discharge resistors, free wheeling diodes

50
Q

List to items that utilize mutual induction

A

Motors and car ignitions

Construction Electrician Level 2 (2 decks)

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