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SUMMER 2024: Radiographic Equipment > Week 5: Magnetism and Electromagnetism > Flashcards

Week 5: Magnetism and Electromagnetism Flashcards

1
Q

Magnetism

A

• Materials that can attract iron are classified as having a strong magnetic force.
• When a charged particle (electron) is in motion, a magnetic force field perpendicular to the motion will be created. The intensity of the magnetic field is represented by imaginary lines. The perpendicular magnetic force is called the orbital magnetic moment.

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2
Q

The perpendicular magnetic force is called the

A

orbital magnetic moment

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3
Q

A magnetic effect is also established by electrons spinning on their axes and this is termed the

A

spin magnetic moment

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4
Q

What are the invisible force fields that are created by a magnet called? When do they occur?

A

-Lines of flux, lines of induction, magnetic field lines, magnetic lines of induction, etc
-They occur when magnetic dipoles orient to create a magnet. The stronger the magnetic field, the more lines of flux, and the higher the flux density

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5
Q

The small magnet created by an electron orbit is called a

A

magnetic dipole

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6
Q

T or F: In nonmagnetic objects, the magnetic dipoles are randomly arranged

A

True

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7
Q

An accumulation of many dipoles aligned creates a

A

magnetic domain

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8
Q

T or F: Dipoles orientate themselves in different directions in the magnetized object creating a magnetic domain

A

False, same direction

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9
Q

The imaginary lines of the magnetic field leave the north pole and enter the south pole, this is called

A

Magnetic laws

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10
Q

Repulsion-attraction

A

Like poles repel, unlike poles attract. In addition, like lines of force repel and unlike lines of force attract, when placed in each other’s force fields

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11
Q

Inverse square law

A

Exactly with electrostatics, as an object gets further away, the influencing field decreases because of the increased area it affects. The force between two magnetic fields is directly proportional to the product of their magnitudes and inversely proportional to the square of the distance between them

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12
Q

Magnetic poles

A

Every magnet has two poles, a north and south. If a single magnet is broken into smaller pieces, smaller magnets are the result

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13
Q

When a nonmagnetized iron bar is brought within the lines of force of a strong magnet, the dipoles will temporarily

A

align themselves with the lines of force passing through the iron bar

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14
Q

If the iron bar is removed from the field after a short time, the dipoles will return to their random orientation, thus leaving the iron bar unmagnetized. This process is called

A

magnetic induction

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15
Q

T or F: The nonmagnetized iron bar is only a magnet while it is being induced

A

True, this is a temporary magnet

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16
Q

T or F: Some objects, if tempered by heat or exposed to a magnetic field for a long period, can retain their magnetism

A

True, this is a permanent magnet

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17
Q

Magnetic induction

A

The iron bar (ferromagnetic) object is in close proximity to a magnet. The lines of flux from the magnet deviate into ferromagnetic iron creating a temporary magnet

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18
Q

Permeability

A

The ease with which a material can be magnetized

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19
Q

Retentivity

A

ability of a material to stay magnetized

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20
Q

Ferromagnetic

A

Can be strongly magnetized; highly permeable, high retentivity, and greatly susceptible to induction

Examples- iron, cobalt, nickel

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21
Q

Paramagnetic

A

Weakly attracted to a magnetic field; low permeability

Examples- platinum, aluminum, gadolinium (MRI contrast agent)

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22
Q

Diamagnetic

A

Weakly repelled by a magnetic field

Examples- water, plastic

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23
Q

Nonmagnetic

A

Not affected by magnetic fields.

Examples- wood, glass, rubber, plastic

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24
Q

Electromagnetism

A

Science of charge and of the forces and fields associated with the charge; branch of physics that deals with the electromagnetic force that occurs between electrically charged particles

25
Q

Han’s Oersted’s Experiment

A

•His experiment proves that when there is no current flowing in a wire, the compass needle aligns itself with the earth’s weak magnetic field. When current is flowing in a wire, the compass needle is deflected toward the wire. When the current stops, the needle returns to the alignment with the earth’s weak magnetic field.
•This experiment led to the conclusion that any moving charge produces a magnetic field.

26
Q

What did the Han’s Oersted’s Experiment conclusion lead to?

A

This experiment led to the conclusion that any moving charge produces a magnetic field

27
Q

Han’s Oersted’s Experiment: With no electric current (electron movement), the compass points _______

A

North

28
Q

Han’s Oersted’s Experiment: With electric current (electron movement), the compass points toward the _____

A

Wire

29
Q

Solenoid (coil of wire)

A

If a series of loops are made, creating a coil, the lines of flux increase in number around the coil (flux density increases). When current flows through this type of coil, it is called a solenoid.

30
Q

Electromagnet

A

solenoid that is wrapped around an iron core (ferromagnetic core). This iron core will serve to increase the flux density even more

31
Q

The strength of solenoids and electromagnets is determined by the

A

-Number of loops (or turns) of wire
-The current strength
-The permeability of the core

32
Q

A magnetic field can create current in a conductor if there is ________ __________ between the two. This is electromagnetic induction.

A

relative motion

33
Q

T or F: Without relative motion between the magnetic field and the conductor, current cannot be created in a conductor.

A

True

34
Q

Current is expressed in _________ and can be measured with an __________

A

amperage, ammeter

35
Q

3 ways to create the motion between the lines of force and a conductor:

A

• Move the conductor through a stationary, unchanging-strength magnetic field
• Move magnetic lines of force through a stationary conductor with an unchanging-strength magnetic field
• Vary the magnetic flux strength from a stationary magnet through a stationary conductor. As the flux strength varies, the lines of force will expand and contract, creating the relative motion to induce current

36
Q

4 factors that regulate the strength of induced current when magnetic lines of force and a conductor are in motion relative to each other:

A

• Strength of the magnetic field
• Speed of the motion between the lines of force and the conductor
• Angle between the magnetic lines of force and the conductor
• Number of turns in the conducting coil

37
Q

Primary coil

A

coil supplied with AC; it is an electromagnet

38
Q

Secondary coil

A

coil in which AC is induced

39
Q

Mutual induction

A

Occurs when two coils are placed in close proximity, and AC supplied to the primary coil induces a similar current flow in the secondary coil. The constantly expanding and contracting magnetic field lines created in the primary coil provides the relative motion, with induction occurring in the secondary coil.

40
Q

Generator (Dynamo)

A

A device that converts mechanical energy to electrical energy & produces alternating current (AC)

41
Q

How does the generator dynamo work?

A

As the wires of the armature rotate, they cut through the magnetic lines of flux of the magnet and produce electrical current in the circuit. The slip rings and brushes allow the armature to rotate while maintaining contact with the wires of the circuit. If the armature is rotated by a strong source of mechanical energy such as steam or water turbine, the generator can produce large amounts of electrical energy.

42
Q

Generator (Dynamo): 0°- 45°

A

no voltage (emf) is produced, but as the armature rotates towards 45° voltage (emf) is beginning to increase in the circuit as the armature turns through the magnetic field

43
Q

Generator (Dynamo): 45°- 90°

A

as the armature rotates through the magnetic field, voltage is increasing and at 90°, the motion of the armature is at the maximum angle and peak voltage (emf) is reached at 90°

44
Q

Generator (Dynamo): 90°-135°

A

as the armature rotates through the magnetic field, voltage (emf) is decreasing

45
Q

Generator (Dynamo): 135°-180°

A

as the armature rotates through the magnetic field, voltage (emf) is decreasing. With the armature’s position at 180°, 0 voltage (emf) is being produced at that moment

46
Q

Generator (Dynamo): 180°-215°

A

beginning at 180° the current is now traveling the opposite direction in the circuit as it was traveling from 0°-180°. At 180°, no voltage (emf) is produced, but as the armature rotates towards 215°, voltage (emf) is beginning to increase in the circuit as the armature turns through the magnetic field

47
Q

Generator (Dynamo): 215°-270°

A

-as the armature rotates through the magnetic field, voltage is increasing and at 270°, the motion of the armature is at the maximum angle and peak voltage (emf) is reached at 270°
-The only difference between 90° and 270° is the direction of current traveling through the circuit, peak voltage is equal at these two points

48
Q

Generator (Dynamo): 270°-315°

A

as the armature rotates through the magnetic field, voltage (emf) is decreasing

49
Q

Generator (Dynamo): 315°-360°

A

as the armature rotates through the magnetic field, voltage (emf) is decreasing. With the armature’s position at 360°, 0 voltage (emf) is being produced at that moment.

-0 voltage (emf) is produced at 0°, 180°, & 360°
-Peak voltage is produced at 90° & 270°

50
Q

One cycle

A

One complete turn of the armature through the magnetic field represents 1 cycle

51
Q

Half cycle

A

from 0°-180° is the positive half cycle, and from 180° to 360° is the negative half cycle. The only difference between the positive half cycle and the negative half cycle is the direction of current flow in the circuit

52
Q

The frequency of the sine wave is determined by what? What is the unit?

A

-Number of cycles per second (cps)
-The unit of frequency is the hertz (Hz)

53
Q

1 cps = __ Hz

A

1

54
Q

American generators operate at ___ Hz

A

60

55
Q

With 60 Hz generators, the current changes directions ____ times per second

A

120 (60 positive half cycles & 60 negative half cycles)

56
Q

Peak voltage occurs at ____ and ____

A

90° and 270°

57
Q

The only difference between 90° and 270° is the

A

direction of current flow in the circuit

58
Q

-0 voltage (emf) is produced at ___, ____, ____ degrees
-Peak voltage is produced at ___ and ____ degrees

A

-0°, 180°, & 360°
-90° & 270°

59
Q

Electromagnetic induction may best be defined as

A

Producing current and voltage in a conductor as it passes through a magnetic field

SUMMER 2024: Radiographic Equipment (11 decks)

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