Chapter 7 Electricity

Question 1

The electric motor is a machine that can transform electricity into…

Answer 1

Rotary motion to perform useful work

Question 2

Faraday used oersted’s principle to …

Answer 2

Build the worlds first electric motor

Question 3

A turning or twisting force that causes rotation is…

Answer 3

Torque

Question 4

What are the four principle parts that make up a D.C. Motor

Answer 4

Magnetic field, movable conductor, a commutator, and brushes

Question 5

We can make the basic D.C. Motor start by itself by giving it what

Answer 5

An armature that contains two or more loops

Question 6

What is the rotating element of a D.C. Motor

Answer 6

The armature

Question 7

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

Answer 7

Risers

Question 8

Brushes are made of

Answer 8

Conductive material such as carbon with a good deal of graphite in it

Question 9

Brushes are made to

Answer 9

Wear out faster then the commutator because it is cheaper and easier to replace brushes then service the armature

Question 10

The field assembly consists of…

Answer 10

Pole pieces and field coils

Question 11

Most motor housings consist of what parts

Answer 11

Field frame, and two end frames

Question 12

The rotor or armature core is made of laminated soft steel to minimize what

Answer 12

Eddy current and hysteresis losses

Question 13

Lap windings are used for what

Answer 13

Low voltage, high current motors

Question 14

Wave windings are for

Answer 14

High voltage low current motors

Question 15

The cemf opposes

Answer 15

Line voltage

Question 16

Cemf counter electromotive force tends to regulate what

Answer 16

Motor speed

Question 17

When a load is put on a motor it slows down which reduces cemf but then increases what

Answer 17

Emf electromotive force

Question 18

Power output is a measure of mechanical power and is expressed in…

Answer 18

Horsepower ratings

Question 19

When a motor has no load it needs little torque and so speeds up to build up cemf in order to blank the armature current and thus the torque

Answer 19

Reduce

Question 20

Series motors are useful where sudden changing loads are put on the motor like

Answer 20

Cranes, hoists, subway trains

Question 21

To reverse the direction of rotation of a D.C. Motor you have to reverse either the…

Answer 21

Field or the armature current

Question 22

Starters are needed to limit the armature….

Answer 22

Current that flows when the motor is turned on

Question 23

Type of controller used to operate a motor driven device that needs to be constantly changed in direction and speed

Answer 23

Drum controller

Question 24

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

Answer 24

Synchronous speed

Question 25

On synchronous motors they use blank windings on their rotor which produce an increase in the magnetic induction between stator and rotor

Answer 25

Damper windings

Question 26

The starting torque of a three phase synchronous motor is...

Answer 26

Zero

Question 27

How can synchronous motors be made self starting

Answer 27

By putting a damper winding over their regular wound rotor

Question 28

Synchronous motors use blank blank to magnetize their rotors

Answer 28

Magnetic induction

Question 29

Induction motors use blank blank to magnetize their rotors

Answer 29

Electromagnetic induction

Question 30

The squirrel cage is located on the

Answer 30

Rotor

Question 31

For the induction motor to work the rotor must slip and turn at a rate slightly blank than that of the blank field

Answer 31

Less/rotating

Question 32

The double squirrel cage rotor provides higher ....

Answer 32

Starting torque

Question 33

The wound rotor motor differs from other induction motors in that it uses resistance in series with its rotor windings through a

Answer 33

Slip ring and brush arrangement

Question 34

The stator and rotor of an induction motor act like windings of a....

Answer 34

Transformer

Question 35

Since the induction motor relies on electromagnetic induction, it's rotor cannot run at the...

Answer 35

Synchronous speed

Question 36

What is created when the molecules of an iron bar remain aligned in an external magnetic field after the position of the bar in the field has been changed

Answer 36

Hysteresis losses

Question 37

A typical hysteresis motor uses what kind of steel in its rotor

Answer 37

Cobalt steel

Question 38

The ac repulsion motor resembles a blank motor and an blank motor

Answer 38

D.C., induction

Question 39

The repulsion start induction motor starts just like a standard repulsion motor, but it converts and runs as a blank blank induction motor with a wound rotor

Answer 39

Single phase

Question 40

Universal motors are fractional horsepower ac series motors specially designed for use on what kind of power

Answer 40

Either D.C. Or ac power

Question 41

The hysteresis synchronous motor develops greater

Answer 41

Torque

Question 42

The repulsion start induction motor begins as a repulsion motor but runs as a...

Answer 42

Wound rotor motor