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Pre-Employment Electrician Theory > Magnetism And Electromagnetism 030103c > Flashcards

Magnetism And Electromagnetism 030103c Flashcards

1
Q

What are Ferromagnetic materials?

Objective 1 Page 2

A

Metals magnetized easily.

Examples are iron, nickel, cobalt and manganese

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2
Q

What are Paramagnetic materials?

Objective 1 Page 2

A

Metals that can be magnetized but not as easily as ferromagnetic metals.

Examples are platinum, titanium and chromium.

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3
Q

What are Diamagnetic materials?

Objective 1 Page 2

A

Metals or non-metals that cannot be magnetized.

Examples are copper, brass, antimony.

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4
Q

What is magnetism?

Objective 1 Page 2

A

A measurable characteristic of a moving electrical charge.

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5
Q

What is known as a magnetic moment?

Objective 1 Page 2

A

When an atoms electron arrangement results in a value of magnetism greater than zero in one direction.

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6
Q

What is a group of atoms all with their magnetic moments in the same direction called?

Objective 1 Page 3

A

Magnetic Domain

Magnetism is increased because the magnetic effect is cumulative.

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7
Q

What are the two types of magnets?

Objective 1 Page 3

A

Temporary

Permanent

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8
Q

What is a temporary magnet?

Objective 1 Page 3

A

When magnet domains are aligned only while they are subjected to a magnetizing force.

Used in door chimes, relays, contactors and motors.

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9
Q

What is a permanent magnet?

Objective 1 Page 4

A

A magnet that does not need to be near a magnetizing force to produce a magnetic effect.

Used in speakers, megohmmeters, analog meters, magnetos and permanent magnet motors.

Alnico 5 is the most common material to be added to high carbon steels to make a permanent magnet.

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10
Q

What location has the greatest ability to attract other materials?

Objective 1 Page 4

A

Magnetic Poles

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11
Q

What direction do lines of force flow outside a magnet?

Objective 1 Page 5

A

From North to South

Flow South to North inside the magnet.

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12
Q

What are the two behaviours of the lines of force of a magnet?

Objective 1 Page 7

A

They do not cross each other

They take the path that best supports lines of force.

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13
Q

What is Magnetic Flux?

Objective 2 Page 8

A

Lines of force around a magnet.

Symbolized by the Greek capital letter phi (Φ)

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14
Q

What is Flux Density?

Objective 2 Page 8

A

The number of magnetic lines of force per unit area.

Symbolized by the Greek letter β (beta)

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15
Q

What is Reluctance?

Objective 2 Page 9

A

The opposition of a material to carry magnetic flux.

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16
Q

What is Permeability?

Objective 2 Page 9

A

The ability of a material to concentrate flux as compared to air.

Examples: Soft Iron has high permeability.
Air has low permeability.

Symbolized by the Greek letter μ (mu)

17
Q

What is Residual Magnetism?

Objective 2 Page 9

A

The magnetic effect that remains in a material after the magnetizing force has been removed.

18
Q

What is Retentivity?

Objective 2 Page 10

A

The level of ability of a material to retain residual magnetism.

19
Q

What is Saturation?

Objective 2 Page 11

A

When an increase in a magnetizing force will not produce an increase in magnetism within a material.

All magnetic domains have been aligned.

20
Q

How does current impact magnetic lines of force around a conductor?

Objective 3 Page 13

A

The strength of the magnetic field and the flux density near a current carrying conductor is directly proportional to current flow.

If current is increased the number of lines of force around the conductor also increases.

21
Q

What three factors affect the strength of a magnetic field produced by a coil?

Objective 3 Page 17

A

The amount of current in the coil.

The number of turns on the coil.

The type of core that is part of the magnetic circuit.

22
Q

What property should the material used for a coil core have?

Objective 3 Page 18

A

Low retentivity.

23
Q

What is the heat produced by the flipping of magnetic demains in a coil core material called?

Objective 3 Page 18

A

Hysteresis Losses.

24
Q

How can Hysteresis losses be reduced? Why?

Objective 3 Page 18

A

Adding Silicon to the steel core material.

The silicon allows the magnetic domains to move within the core material with less friction.

25
Q

What are Eddy Currents?

Objective 3 Page 18

A

Voltages that are induced in conductive materials of an electromagnetic device subjected to a changing magnetic field.

26
Q

What are Eddy Current Losses?

Objective 3 Page 19

A

The heat produced and subsequent energy lost due to circulating currents.

27
Q

How can Eddy current losses be reduced?

Objective 3 Page 19

A

By having a core made of thin insulated sheets instead of a solid construction.

28
Q

What is Faraday’s Law Of Induction?

Objective 4 Page 22

A

States the amount of voltage induced in a conductor is proportional to the rate at which the conductor cuts the lines of force.

Cut more flux, get more volts.

29
Q

How many lines of force need to be cut per second by a conductor to induce 1 Volt?

Objective 4 Page 22

A

100 Million lines per second.

30
Q

What factors affect the amount of induced EMF?

Objective 4 Page 24

A

Flux density

Number of turns in the conductor

The rate at which lines of force are cut. Angle at which they are being cut. 90 degrees would be maximum voltage.

31
Q

What does Lenz’s Law Of Induction state?

Objective 5 Page 27

A

An induced voltage will cause a current to flow in such a direction that its magnetic effect will oppose the change that produced it.

Induced EMF will be opposite to source polarity.

32
Q

What is Inductance?

Objective 5 Page 29

A

The property of an electric circuit that opposes a change of current in that cirucit.

33
Q

What is Mutual Induction?

Objective 5 Page 30

A

Takes place when a changing current in one circuit causes a voltage to be induced into another separate circuit.

Pre-Employment Electrician Theory (8 decks)

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