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RWD OP 1ST 6 MONTHS > Electricity 7 Of 7 > Flashcards

Electricity 7 Of 7 Flashcards

1
Q

Faraday used Oersted’s discovery, that electricity could produce motion, to build the worlds first ______________ in 1821.

A

Electric motor

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2
Q

What is the left hand rule?

A

It shows the direction of the flux lines around a wire that is carrying current.

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3
Q

What is the right hand rule for motors?

A

It shows the direction that a current carrying wire will be moved in a magnetic field.

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4
Q

What fingers point to what when using the right hand rule for motors.

A

Middle finger points in direction of current.
Forefinger=magnetic field
Thumb= motion of the conductor.

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5
Q

The four principle parts of an elementary dc motor are?

A

1-magnetic field
2-a movable conductor
3-a commutator
4- brushes

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6
Q

You can make the basic dc motor start by itself by giving it an armature that contains?

A

Two or more loops.

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7
Q

The ___________ is the rotating element of the dc motor.

A

Armature

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8
Q

The leads from the armature coils are connected to the raised portions of the commutator segments known as __________.

A

Risers

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9
Q

Brushes are made of soft carbon material containing a large amount of?

A

Graphite

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10
Q

Why are brushes designed to wear out faster than the armature?

A

Because they are cheaper to replace than to service the armature.

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11
Q

The field assembly in a dc motor consists of ______________ and ___________.

A

Pole pieces

Field coils

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12
Q

Most motor housings contain these three parts?

A

A field frame and two end frames

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13
Q

What are lap windings used for?

A

Low-voltage, high-current motors

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14
Q

What are wave windings used for?

A

High-voltage, low-current motors

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15
Q

What is cemf.

A

Counter electromagnetic force

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16
Q

Since the _________ opposes the line voltage, it acts to cut down the short circuit current through the _______ resistance armature.

A

Cemf, low

17
Q

What gives electric motors a built in system for regulating their own speed?

A

CEMF

18
Q

What happens to the motor when a loads is connected?

A

Motor slows down
Cemf goes down
EMF goes up
Speed goes up

19
Q

Motors are rated in terms of the load they can drive. What is the rating called?

A

Their power output.

20
Q

Power output is a measure of _________ Power delivered by the motor at full load and is given in ____________.

A

Mechanical power,

Horsepower

21
Q

When a series motor has no load in needs little _________.

A

Torque

22
Q

How does a series motor with no load reduce armature current?

A

By speeding up to build up cemf to reduce the armature current

23
Q

Series motors are used when?

A

Sudden changing loads are put on the motor.

24
Q

How do you reverse the direction of a dc motor?

A

Reverse either the field or the armature current, but not both

25
Q

The _________ makes it easy to operate a motor-driven device that needs to be constantly changed in direction and speed.

A

Drum controller

26
Q

The natural rate at which the magnetic field rotates about the stator is called?

A

The synchronous speed

27
Q

What does a stator have that insures a rotating magnetic field is created.

A

Shaded poles

28
Q

As the stator field rotates, the _________ is dragged along at this synchronous speed.

A

Rotor

29
Q

Single phase motors can be started by hand, or they can be made with damper windings on their rotor to be?

A

Self starting

30
Q

A two-pole motor with 60hz freq. has a synchronous speed of ____________.

A

3600 rpm

Rpm= (Hz x 120)/#of poles

31
Q

For the induction motor to work, the rotor must __________ and ______ and a rate slightly less than that of the rotating field.

A

Slip

32
Q

What does the double squirrel cage provide?

A

Higher starting torque

33
Q

The stator and rotor of an induction motor act like?

A

Windings of a transformer

34
Q

Since the induction motor relies on electromagnetic induction, it’s rotor cannot?

A

Run at synchronous speed

35
Q

How are hysteresis losses created?

A

When molecules of an iron bar remain aligned after the position of the bar in the field has been changed

36
Q

How does a ac repulsion motor resemble a dc motor?

A

It has a:

Drum-wound armature, a commutator, and brushes.

37
Q

How does a ac repulsion motor resemble an induction motor?

A

I has a stator with distributed windings.

38
Q

The hysteresis synchronous motor uses a _______ rotor to develop a greater torque.

A

cobalt-steel

RWD OP 1ST 6 MONTHS (16 decks)

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