ASNT Magnetic Particle Testing > Chapter 1 & 2: Study Guide Summary > Flashcards

Chapter 1 & 2: Study Guide Summary Flashcards

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1
Q

What does reluctivity refer to?

A

The reciprocal of permeability

It is a measure of how much a material opposes the magnetic field.

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2
Q

What is the unit of measurement for B in magnetic particle testing?

A

Teslas

B represents the flux density resulting from variations in the magnetizing force.

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3
Q

Where is the magnetic field strongest in a coil?

A

On the inside surface of the coil

The field is essentially parallel to the axis of the coil.

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4
Q

How do the magnetic fields around each turn of a coil behave?

A

They combine to form a unified field

This unification enhances the overall magnetic effect of the coil.

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5
Q
A
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6
Q

Fill in the blank: Flux density is defined as the number of lines of flux intercepting an area ______ to the flux.

A

perpendicular

This definition emphasizes the orientation of the area in relation to the magnetic field.

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7
Q

What is the significance of flux density in magnetic fields?

A

It indicates the relative strength of the field in various regions of the affected space

Magnetic field strength varies throughout the space influenced by a magnetic field.

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8
Q

What is the term for the residual magnetic flux that remains when the magnetizing force is reduced to zero?

A

Remanence

It results from magnetic domains still aligned in the magnetized direction.

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9
Q

Define solenoids.

A

Coils where the length is greater than the diameter

Solenoids have specific geometric properties that influence their magnetic fields.

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10
Q

What generates microscopic electric currents within an atom?

A

The motion of electrons

An electron moving in orbit around a nucleus generates an electric current.

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11
Q

What happens when like poles of magnets are brought close together?

A

They repel each other

Unlike poles attract one another.

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12
Q

What is measured by the magnetic moment of an electron?

A

The strength of the electric current generated by the orbiting electron

All electrons in motion create a current with an associated magnetic field.

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13
Q

What is longitudinal magnetization?

A

When the longitudinal axis of the part is parallel to the axis of the coil

This orientation maximizes the magnetic effect.

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14
Q

How is H measured for coils in magnetic testing?

A

Ampere turns per meter

If the magnetomotive force is given in amperes, H is shown in amperes per meter.

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15
Q

What is the relationship between the direction of the magnetic field and the direction of current flow?

A

Perpendicular

This concept is defined as the right-hand rule.

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16
Q

What happens to the magnetic field when the current is removed from a ferromagnetic material?

A

The field continues to exist but is less intense

The intensity is linear along the length of the conductor if the material is uniform and homogeneous.

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17
Q

How can a circular magnetic field be induced into a hollow cylinder?

A

By placing a current-carrying conductor inside the cylinder

The circular magnetic field around the conductor induces a circular field in the magnetic material.

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18
Q

True or false: Lines of force are real physical entities in magnetic fields.

A

FALSE

Lines of force are imaginary lines used to visualize the direction and shape of the magnetic field.

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19
Q

What does the hysteresis curve represent in magnetic particle testing technology?

A

The relationship between flux density (B) and magnetizing force (H)

B is plotted on the vertical axis and H on the horizontal axis.

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20
Q

What is the result of indirect (induced) magnetization?

A

A ferromagnetic material is influenced by an external magnetic field

This field can be created by permanent magnets or electromagnetic devices.

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21
Q

Where is the magnetic field strongest in a coil?

A

On the inside surface of the coil

The magnetic field is essentially parallel to the axis of the coil.

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22
Q

What defines a solenoid?

A

Length greater than diameter

Solenoids are a specific type of coil.

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23
Q

The relationship between permeability (μ), magnetic flux density (B), and magnetizing force (H) is evaluated through what?

A

the hysteresis curve

The hysteresis curve illustrates how permeability varies with the intensity of the applied force.

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24
Q

What happens to a ferromagnetic material when heated above the Curie point?

A

Above the Curie point, steel (which is primarily composed of iron) loses its ferromagnetic properties and becomes paramagnetic, not diamagnetic.

At this temperature, the magnetic domains are randomly oriented.

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25
What is **retentivity**?
The ability of materials to retain magnetism after the magnetizing force has been removed ## Footnote It is a key characteristic of magnetized materials.
26
What is the **fundamental law** of the magnetic effects of electric currents formulated by Andre-Marie Ampere?
Electric current is a positive charge flowing from positive to negative ## Footnote Modern theory shows that the negatively charged electron is responsible for electric current.
27
Define **diamagnetic materials**.
Materials with a negative relative permeability slightly less than one ## Footnote Examples include mercury, gold, bismuth, and zinc.
28
Which elements are considered **ferromagnetic**?
* Iron * Cobalt * Nickel * Gadolinium ## Footnote Gadolinium is included despite not being an engineering material because it is strongly ferromagnetic at lower temperatures.
29
30
What is the **Barkhausen effect**?
Step magnetization of ferromagnetic material ## Footnote It occurs as magnetic domains align with an external field.
31
What is the **coercive force** of a material?
The magnetizing force energy required to reduce remanence flux density to zero ## Footnote The material is not completely demagnetized until heated above the curie point.
32
What is **permeability** in the context of magnetism?
The ease with which a material can be magnetized ## Footnote Permeability is characterized by the relationship between magnetic flux density (B) and magnetizing force (H) and is evaluated through the hysteresis curve.
33
What are the two classifications of techniques used to magnetize **ferromagnetic materials**?
* Direct magnetization * Indirect (induced) magnetization ## Footnote These techniques produce a magnetic field in the material.
34
What type of materials are used in **electronic equipment** and cores for coils in eddy current probes?
* Manufactured ferrites * Magnetic particles ## Footnote These materials have very low retentivity and very high permeability.
35
What is the **curie point**?
The temperature above which magnetized material becomes completely demagnetized ## Footnote It remains demagnetized if cooled from temperatures above the curie point without influence from magnetic fields.
36
In **direct magnetization**, what is established when electric current flows through a conductor?
An encircling magnetic field ## Footnote The magnetic field is uniform along the length of a straight conductor.
37
What is the **hysteresis curve** or **hysteresis loop**?
The closed curve formed by the paths a, b, c, d, e, f, a ## Footnote It represents the relationship between magnetizing force and flux density during magnetization and demagnetization.
38
List the **properties of magnetic lines of force**.
* They form closed loops * They do not cross one another * They seek paths of least magnetic resistance * Their density decreases as distance from the poles increases * They have direction from north to south external to the magnet ## Footnote These properties help visualize and understand magnetic fields.
39
What is defined as **μmax**?
The maximum permeability of the material ## Footnote It is determined by drawing a line from the origin to a point tangential to the hysteresis curve.
40
What must be ensured when using **direct magnetization techniques** to prevent arcing?
Good electrical contact ## Footnote This is crucial to avoid burning of the material.
41
What is the **remanence** or **residual field** in a magnetized material?
The net magnetic flux remaining when H reaches 0 ## Footnote This occurs because not all magnetic domains have reversed their alignment.
42
What is **Faraday’s law of magnetic induction**?
When matter is placed in an external magnetic field, it produces its own macroscopic magnetic field ## Footnote This occurs when the magnetic moments of the material’s electrons become reoriented.
43
In the magnetic hysteresis loop, what does the horizontal axis represent?
Magnetizing force H ## Footnote H is the magnetomotive force per unit length.
44
What type of materials are used for **permanent magnets**?
* Alnico * Materials with high retentivity and permeability Alnico is a type of alloy primarily composed of aluminum (Al), nickel (Ni), and cobalt (Co)—hence the name Al-Ni-Co. It may also include iron and small amounts of other elements like copper or titanium, depending on the specific grade. ## Footnote These materials have very open loops in the hysteresis curve.
45
What is **permeability** in the context of magnetism?
The ease with which a material can be magnetized ## Footnote Permeability indicates how well magnetic lines of force can pass through a material.
46
**How do the magnetic fields** around each turn of a coil behave?
Combine to form a unified field ## Footnote This unification enhances the overall magnetic effect.
47
What is the **curie point** or **curie temperature**?
The temperature above which magnetized material becomes completely demagnetized ## Footnote It remains demagnetized if cooled from temperatures above the curie point, uninfluenced by magnetic fields during cooldown.
48
What is the difference between **flux** and **flux density**?
Flux: Number of lines of force in a magnetic field Flux Density: Number of lines of flux perpendicular to an area ## Footnote Flux density is more significant for practical applications.
49
What is the term for when a material is said to be **magnetically saturated**?
When further increase in magnetizing force produces little change in B ## Footnote This indicates that the material cannot be magnetized further in the same direction.
50
What does the term **flux** indicate in relation to magnetic fields?
The number of lines of force associated with a magnetic field at a specific point or within a defined area ## Footnote Total flux is rarely of any practical concern.
51
The intensity of the **magnetic field** surrounding a conductor is in direct proportion to what?
Current (amperes) ## Footnote It diminishes inversely with increasing distance from the conductor.
52
What is the effect of using a **bar magnet** for magnetization?
An opposite magnetic pole is established in the material ## Footnote The induced lines of force seek to close with the pole at the opposite end of the inducing magnet.
53
What characterizes **paramagnetic materials**?
Small positive susceptibility and positive relative permeability slightly more than one ## Footnote Examples include aluminum, platinum, copper sulfate, and wood.
54
**What is direct magnetization**?
Passing current directly through the part ## Footnote This creates a circular magnetic field.
55
The strength of the magnetic field in a hollow cylinder can be controlled by adjusting the _______.
Electrical current in the conductor ## Footnote This allows for the entire volume of the cylinder to be magnetized.
56
What type of materials are used for **permanent magnets**?
* High retentivity * High permeability ## Footnote Examples include materials like alnico, which have open loops in their hysteresis curve.
57
What is the common shape of permanent magnets used for magnetic induction?
U-shaped (horseshoe magnets) ## Footnote These magnets create a straight induced field between the two poles.
58
What defines **ferromagnetic materials**?
High positive susceptibility and high positive permeability much greater than one ## Footnote They consist of small areas called domains that align with an external magnetic field.
59
What is the basic composition of **matter**?
* Atoms * Positively charged protons * Negatively charged electrons ## Footnote Matter is composed of atoms, which have protons in the nucleus and electrons in motion around them.
60
Equation to calculate flux density
61
What is **flux density**?
The number of lines of flux transverse (perpendicular) to an area ## Footnote Flux density is of greater practical importance than total flux.
62
What can be described by examining the **magnetic hysteresis loop**?
Magnetic properties of materials ## Footnote The hysteresis loop provides insights into how materials respond to magnetic fields.
63
What are **coils** formed by?
A number of loops ## Footnote Coils are conductors that create magnetic fields.
64
**What is indirect magnetization**?
Induction of a longitudinal field into a bar of magnetic material ## Footnote This contrasts with direct magnetization, where current passes directly through the part.
65
As the magnetizing force **H** decreases to 0, what happens to the **flux density** values?
They follow the path from a to b ## Footnote This path represents the field removal portion of the curve.
66
What happens to parts placed within the coil?
They are magnetized in a direction parallel to the coil’s magnetic field ## Footnote This is known as longitudinal magnetization.
67
**What is longitudinal magnetization**?
When the longitudinal axis of the part is parallel to the axis of the coil ## Footnote This alignment ensures effective magnetization.
68
What are the two classifications of magnetization techniques?
* Direct magnetization * Indirect (induced) magnetization ## Footnote Direct magnetization involves passing electric current through the part, while indirect magnetization is influenced by an external magnetic field.
69
When a straight conductor is formed into a **loop or coil**, how does the direction of the magnetic field change?
It becomes perpendicular to the plane of the coil ## Footnote The coil’s magnetic field outside forms a toroid.
70
71
What is the **initial condition** of a ferromagnetic material before magnetization?
Not magnetized or fully demagnetized ## Footnote This condition allows for the observation of the material's response to magnetizing forces.
72
The formula for calculating **flux density** is given by which equation?
B = Φ / A ## Footnote Where Φ is magnetic flux in webers and A is the area perpendicular to the flux in square meters.
73
**What are coils** formed by?
A number of loops ## Footnote Coils are conductors that create magnetic fields.
74
What is the relationship between **direct magnetization** and the circular field produced by passing current through the part?
The field is essentially perpendicular ## Footnote Direct magnetization occurs when current flows directly through the part.
75
Magnetic lines of force concentrate more in a piece of iron than in __________.
air or in a nonmagnetic material ## Footnote This concentration occurs when the iron is placed between the poles of a magnet or within a magnetic field.
76
**What does a longitudinal magnetic field produced by a coil induce**?
A longitudinal field into a bar of magnetic material ## Footnote This occurs when the bar is placed within the coil and parallel to its center line.
77
In **direct magnetization**, what is passed through the part to create a magnetic field?
An electric current ## Footnote The part acts as a conductor of the electric current.
78
What happens to the magnetic field when an electric current flows through a **conductor**?
An encircling magnetic field is established both within and outside the conductor ## Footnote The field is uniform along the length of a straight conductor.
79
What type of magnets can magnetize ferromagnetic materials through close proximity or direct contact?
Permanent magnets ## Footnote An opposite magnetic pole is established in the material being magnetized.
80
At point **a** on the hysteresis curve, what happens to the magnetic domains?
Almost all are aligned with the field ## Footnote Further increases in magnetizing force produce little change in flux density.
81
In **magnetic particle testing technology**, which type of materials are of interest?
Ferromagnetic materials ## Footnote Only ferromagnetic materials are relevant for this testing technology.
82
What is **remanence** in magnetic materials?
The residual magnetic field remaining after the magnetizing force is removed ## Footnote This indicates that magnetic domains remain aligned.
83
What type of magnets can induce magnetization in ferromagnetic materials?
* Permanent magnets * Electromagnetic devices ## Footnote Permanent magnets can magnetize materials in close proximity or contact.
84
When using a **bar magnet** to magnetize a bar-shaped material, the field direction is considered _______.
Longitudinal ## Footnote This means the field is parallel to the axis of the part.
85
What is the term for the magnetic field within a conductor when it is a **ferromagnetic material**?
Circular field ## Footnote This field circulates around the axis of the conductor.
86
At point **a** on the magnetization curve, what happens to the **magnetic domains**?
Almost all are aligned with the field ## Footnote This alignment indicates that the material is approaching magnetic saturation.
87
The relationship between **permeability**, **magnetic flux density**, and **magnetizing force** is evaluated through what?
The hysteresis curve ## Footnote Each point along the curve represents a different value for the permeability of the material.
88
The external strength of the magnetic field is directly proportional to the _______ and inversely proportional to the distance perpendicular to the axis of the conductor.
current flow ## Footnote This relationship defines how the magnetic field strength varies with distance.
89
Permeability can be expressed as:
90
**What happens to parts placed within the coil**?
They are magnetized in a direction parallel to the coil’s magnetic field ## Footnote This process is known as longitudinal magnetization.
91
How can a **circular magnetic field** be induced in a hollow cylinder?
By placing a current-carrying conductor inside the cylinder ## Footnote The strength of the magnetic field is controlled by adjusting the electrical current in the conductor.
92
What does a **longitudinal magnetic field** produced by a coil induce?
A longitudinal field into a bar of magnetic material placed within the coil ## Footnote This process is referred to as indirect magnetization.
93
What are the **three commonly encountered magnetic behaviors**?
* Diamagnetism * Paramagnetism * Ferromagnetism ## Footnote Ferromagnetism is the most important for magnetic particle testing.
94
Materials with **closed loops** in their hysteresis curve are characterized by what properties?
* Very small retentivity (b, e) * Small coercive force (c, f) ## Footnote These materials are often used in electronic equipment due to their low retentivity and high permeability.
95
In the hysteresis curve, each point along the curve represents a different value for the **permeability** of that material and is dependent on what?
the intensity of the applied force H ## Footnote This relationship shows how permeability changes with varying magnetizing forces.
96
In the magnetic hysteresis loop, what does the vertical axis represent?
Flux density B ## Footnote B is measured in teslas.
97
What is the **coercive force** or **coercivity** of a material?
The magnetizing force energy required to reduce remanence flux density to 0 ## Footnote This indicates the material's resistance to becoming demagnetized.
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