Big review practice questions

Question 1

Magnetic lines exit one point and enter another. In which direction does this happen?

Answer 1

North to South

Question 2

What is flux density?

Answer 2

concentration of flux lines

Question 3

Name 3 ferromagnetic materials?

Answer 3

Iron
Nickel
Cobalt

Question 4

There are two groups of magnets, what are they?

Answer 4

permanent

temporary

Question 5

What does the term saturation refer to?

Answer 5

Max flux lines

Question 6

The material that the coil is wrapped around determines what?

Answer 6

magnetizing ability

Question 7

What does a high coercive force indicate?

Answer 7

difficulty to demagnetize

Question 8

How is a hysteresis loop formed?

Answer 8

by A/C current

Question 9

The term hysteresis in electrical terminology means?

Answer 9

“to lag” between a change in value or direction

Question 10

Normally how many times per second do the domains in the core undergo a periodic reversal?

Answer 10

60

Question 11

The core will become warm partly due to the constant field of reversal. Some of the energy is being lost due to heat. This is known as a ?

Answer 11

hysteresis loop

Question 12

What size of hysteresis loop would be preferred for motors, transformers, alternators and other equipment used in A/C circuits?

Answer 12

small area

Question 13

Does wood have a high or low reluctance?

Answer 13

high

Question 14

Does iron have a high or low reluctance?

Answer 14

low

Question 15

If AC equipment is an assembly of thin sheets of iron called?

Answer 15

laminations

Question 16

whenever mines if current pass through any kind of metal they generate a current in the metal. What is this current called?

Answer 16

eddy currents

Question 17

Unit for magnetic flux?

Answer 17

weber

Question 18

The amount of residual magnetism depends on the _____________ is the steel used?

Answer 18

retentivity

Question 19

The strength of a magnetic field is represented by the __________ of the lines of force?

Answer 19

density

Question 20

The magnetic strength of a coil can be measured in ____________?

Answer 20

ampere turns

Question 21

Equal magnetizing forces can be produced by ____________ current and few turns or ___________ current and many turns.

Answer 21

large

small

Question 22

When iron oxide is mixed with oxides of manganese, cobalt, nickel, copper or zinc and then is pressed and fired resulting temporary magnetic materials called?

Answer 22

ferrites

Question 23

Unit for flux density?

Answer 23

Tesla

Question 24

Magnetic cores are usually constructed from materials with a high ________ and low ___________?

Answer 24

Permeability

Reluctance

Question 25

The MAGNETIC flux in a circuit is directly proportional to the _____________ and inversely proportional to the ____________ of the magnetic circuit?

Answer 25

mmf

reluctance

Question 26

What is one way to tell the difference between the high voltage leads and low voltage leads of magnetic cores?

Answer 26

size of wire

Question 27

hysteresis losses are caused from what two things?

Answer 27

heat

vibration

Question 28

What is the curie temperature for iron?

Answer 28

770 degrees celsius

1420 Fahrenheit

Question 29

What happens to the flux density when the air gap is widened?

Answer 29

it becomes lower

Question 30

Some of the lines of force leave and enter the coil before reaching the ends of the coil. That is referred to as _________________?

Answer 30

leakage flux

Question 31

Symbol for reluctance?

Answer 31

Rm

Question 32

What is the symbol for magnetizing force?

Answer 32

H

Question 33

Motors convert _________ energy to ___________ energy.

Answer 33

electrical

mechanical

Question 34

Generators convert ____________ energy to _____________ energy.

Answer 34

mechanical

electrical

Question 35

What controls the magnitude of the current through the field coils?

Answer 35

field rheostat

Question 36

motors and generators need magnetic poles. what are these poles called?

Answer 36

field poles

Question 37

The moveable part of a motor or generator is called?

Answer 37

rotor