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Electrical Theory Basics > Unit 18 > Flashcards

Unit 18 Flashcards

1
Q

What are the three main characteristics of an Eddy current?

A

Flow erratically ; consume power ; and increase the opposition to current flow

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2
Q

Because electrons spin, they have their own what?

A

Magnetic fields

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3
Q

What happens as alternating current within a conductor increases, an expanding electromagnetic field field is created through the conductor and the magnetic flux lines cut through the conductor .

A

Voltage is induced within the conductor

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4
Q

The expanding and collapsing magnetic field from an ac circuit induces a voltage in the conductors that repels the flowing electrons towards the surface of the conductor, what is this called?

A

Skin effect

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5
Q

Induced voltage that opposes the current flow is called what?

A

Counter-electromotive force or CEMF

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6
Q

An ac circuit contains inductive reactance because the voltage and current are what with each ohter?

A

Not in phase

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7
Q

In dc circuits, the only property that affects current and voltage flow is _______

A

Resistance

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8
Q

The total opposition to current flow in an ac circuit includes what and what is it called?

A

Resistance and reactance ; impedance

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9
Q

Windings with soft iron cores produce greater self-inductance than windings with an air core because…

A

Iron cores provide an easy path for magnetic flux

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10
Q

This is the property of an electrical circuit that enables it to store electrical energy by a means of an electromagnetic field and to release this energy at a later time

A

Inductance

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11
Q

A self induced voltage waveform is ____ degrees out of phase with the applied voltage waveform

A

180

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12
Q

Will a longer core produce more or less CEMF?

A

Less

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13
Q

CEMF acts to oppose the change in current flowing in the conductor, this property is called what?

A

Inductive reactance

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14
Q

All that is required to induce voltage is a ______ and an external _____ ______ with relative motion between the two

A

Conductor ; Magnetic field

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15
Q

The movement of electrons caused by an external magnetic field is called what?

A

Induced current

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16
Q

Inductive reactance is measured in what?

A

Ohms

17
Q

When alternating current increases, the polarity of the CEMF within the conductors _____ the conductor’s current.

A

Opposes

18
Q

In a purely inductive circuit, the applied voltage waveform ____ the current waveform by _____ degrees

A

Leads ; 90

19
Q

CEFM is ____ proportional to the cross-sectional area of the core and ______ proportional to its lengh

A

Directly ; inversely

20
Q

Besides conductor resistance, alternating current flow contains an additional element called what that opposes the flow of electrons?

A

Reactance

21
Q

When a conductor is coiled into adjacent loops (helically wound), it is called what?

A

A winding

22
Q

Impedance is measured in what and what letter is used as the abbreviation?

A

Ohms ; Z

23
Q

The waveform of the induced voltage in the conductor is ____ degrees out of phase with the circuit current and _____ degrees out of phase with the applied voltage waveform

A

90 ; 180

24
Q

What are the three major uses of induction?

A

Transformers, motors, and generators

25
Q

Conductor resistance is directly proportional to its ________ and inversely proportional to to its ______ ___

A

Length ; Cross-sectional area

26
Q

When alternating current decreases, the polarity of the induced voltage within the conductor _____ the conductor’s current.

A

Aids

27
Q

The amount of the self-induced voltage created within the winding is directly proportional to what three things?

A

Current flow, windings, and frequency

28
Q

The voltage induced within the conductor caused by its own expanding and collapsing magnetic field is known as what?

A

Self-induced voltage

29
Q

(T/F) The induced voltage in a conductor carrying alternating current sometimes opposes the change in current flowing through the conductor.

A

False

30
Q

The associated potential that is established by induced current is called what?

A

Induced voltage

31
Q

When electrons move, their magnetic fields combine to produce an overall magnetic field that extends _______ the conductor.

A

Outside

32
Q

These are small independent currents that are produced as a result of the expanding and collapsing magnetic field from an ac circuit.

A

Eddy currents

Electrical Theory Basics (11 decks)

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