magnetic field. MAGNETISM. ▫ When a charged particle moves, a magnetic filed
is produced around the moving charge. This magnetic field exerts a magnetic ...
Principles of Imaging Science II (120)
Magnetism & Electromagnetism
MAGNETISM
Magnetism is a property in nature that is present when charged particles are in motion. Any charged particle in motion creates a magnetic field
MAGNETISM
When a charged particle moves, a magnetic filed is produced around the moving charge. This magnetic field exerts a magnetic force on certain kinds of particles that are within the field
Moving charge produces a magnetic field Magnetic field of a charged particle is perpendicular to the motion of the particle
Orbital magnetic moment
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MAGNETISM
When a charged particle moves in a circular or elliptical path, the perpendicular magnetic field moves with the charged particle
MOVING CHARGES PRODUCE MAGNETIC FIELD
Every electron has a charge. Everyone of these charges is in motion
Spin magnetic moment: Electron spin on axis
Dipole: Tiny magnetic field created by a single spinning electron. Magnetic domain: Many atoms aligned to produce a larger magnetic field.
Many domains exist in a magnet
MAGNETISM LAWS
Magnetic Poles
North & South Poles Iron filings will concentrate at ends “Flux” lines extending from N – S The greater the concentration of flux lines per unit of measure (m2) the greater the strength of the magnetic field
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MAGNETISM LAWS
Attraction & Repulsion
Similar charges repel, unlike charges attract Imaginary lines of the magnetic field leave the North Pole and enter the South Pole
MAGNETIC CLASSIFICATION (Susceptibility)
Ferromagnetic (Iron, Cobalt, Nickel)
High Permeability
Ability of a material to be magnetized either by the application of electric current or exposure to a magnetic field
High Retentivity
Ability of a magnetized material to remain magnetized once the magnetizing source (electric current or magnet) is withdrawn
MAGNETIC CLASSIFICATION
Diamagnetic (wood, glass, plastic)
No Permeability (non-magnetic) No Retentivity
Cannot be artificially magnetized and are not attracted to a magnet Repel magnetic fields
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MAGNETIC CLASSIFICATION
Paramagnetic (Aluminum)
Low Permeability Low Retentivity
Categorized between ferromagnetic and diamagnetic
Oersted’s Experiment
Discovered that a compass needle is attracted to a wire that carries a current. When the current is OFF, the needle points North, to the earth’s magnetic pole.
Result: Any moving charge produces a magnetic field. However, it is the movement of electrons in the electric current that makes the magnetic field
Oersted’s Experiment
Proved that an electrical current can be used to produce magnetic fields
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SOLENOID
Coil of wire with current flowing through it Magnetic field lines form circles around each section of the wire Used for detent locks on x-ray tube Magnetic field in center can be intensified by placing iron in coils
ELECTROMAGNET
Consists of a loop of wire wrapped around a soft iron core. When electrical current passes through the wire, the iron core becomes a magnet. The strength of the electromagnet is proportional to the
Strength of the current Number of loops surrounding the core
Magnetic Field Lines SOLENOID
ELECTROMAGNET
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ELECTROMAGNETIC INDUCTION
Definition: The result of two coils being placed in close proximity. A varying current is supplied to the first coil, which then induces a similar flow in the second coil. Relies on the principle of interacting electric and magnetic fields
A changing magnetic field produces an electric field The magnetic field must be changing or fluctuating in order for mutual induction to occur
Purpose: To induce an EMF (electromotive force)
ELECTROMAGNETIC INDUCTION
Moving a wire through a magnetic field induces current to flow in the wire
Faraday’s experiment proved that a magnetic field can generate electricity (Opposite of Oersted’s Law)
ELECTROMAGNETIC INDUCTION
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ELECTROMAGNETIC INDUCTION
Strength of Current Depends on:
Strength of magnetic field
speed with which conducting material cuts or is cut by magnetic lines of force
Angle of conductor to magnetic field
Larger magnet yields greater strength
Velocity of magnetic field
Perpendicular better than oblique
Number of turns of wire coil
Greater number of turns produces greater current
TYPES OF CURRENT ALTERNATING CURRENT (AC)
DIRECT CURRENT (DC)
Electrons flow in only one direction
Waveform begins at zero and moves to its maximum potential at its peak
Electrons flow first in one direction (the first half of the cycle), and then in the other direction (the second half of the cycle) U.S. current: 60 Hz AC Waveform represented using a sinusoidal or sine wave
TYPES OF CURRENT
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GENERATORS
Definition: A electromagnetic device that converts mechanical energy to electrical energy
Produces alternating current (AC) with the use of slip rings and an armature
Produces direct current (DC) with the use of a commutator ring in place of the slip rings
GENERATORS
GENERATORS
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ELECTRIC MOTOR
Converts electrical energy to mechanical energy Induction motor to turn the anode at a very high speed to dissipate heat during x-ray production
Consists of rotor and stator
Simple DC Motor
MOTORS
INDUCTION MOTOR The stator is made of stationary electromagnets located around the outside. The rotor, located with the stator, is made of an iron core surrounded by coils. The magnetic field of the stator around the rotor is created by a series of electromagnets. These magnets are turned on and off in a sequence, such that the outside magnetic field itself rotates. The inner coils around the central rotor of the motor are not connected to a current source. Instead, a current is induced in them by the magnetic field of the stator, and this induced current creates the inner magnetic field that attempts to align itself with the stronger outside magnetic field. This force is what turns the rotor.
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Transformers
Designed to change the voltage and current in agreement with Ohm’s Law There is an inverse relationship between voltage and current Control of voltage and current is achieved by a process of Mutual Induction
Transformer Types
Closed Core
Square core of ferromagnetic material Primary coil & Secondary coil at opposite ends
Shell Type
More efficient Center cores with separate primary & secondary windings
Transformer Types
Autotransformer
Single ferromagnetic column core with single coil wrapped around Smaller design
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Transformer
Operate on mutual or self- induction Mutual induction requires alternating current (AC) and 2 coils of electrically conductive material
Generates AC in a 20 coil when AC is applied to the 10 coil Step-Up, Step-Down Transformers
Transformer Law
Designed to alter voltage and current in an AC circuit The ability to control current and voltage is dependent upon:
# windings (turns) on the primary and secondary sides Voltage & Current on the primary side
Transformer Video
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Transformer Law
There is a direct relationship between transformer voltage and the # of primary & secondary turns: Vs = Ns Vp Np
Law Applied
A transformer has 100 primary and 400 secondary turns of wire. What is the secondary voltage if 220 volts are applied to the primary coil? Vs = Ns Vp Np 880 Volts
Transformer Law The inverse relationship between transformer voltage and current is expressed as: Vs = Ip Vp Is Vs = Voltage secondary side Vp = Voltage primary side Ip = Current primary side Is = Current primary side
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Law Applied
A step-down transformer is delivered a total of 220 volts and 3 amps on the primary side. Output voltage is 110 volts what is the output (secondary) current? Vs = Ip Vp Is 6 amps
Transformer Law There is an inverse relationship between transformer current and the # of primary and secondary turns Is Ip
=
Np Ns
Law Applied A transformer has 3,000 turns on the secondary side and 600 windings on the primary side. If 0.5 amps flow through the primary windings, what is the output current on the secondary side? Amps? mA? Is = Np Ip Ns 0.1 amps 100 mA
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