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Chapter 5 Electricity, Magnetism, Electromagnetism
Radiologic Technology (Liceo de Cagayan University)
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CHAPTER 5
ELECTRICITY, MAGNETISM, & ELECTROMAGNETISM
X-ray Imaging System It causes charged particles to move from one
Primary function: to convert electric energy pole to another
into electromagnetic energy Positive charge: points outward
Negative charge: points toward
ELECTROSTATICS
Electrostatic Force
Electrostatics The force of attraction between unlike
The study of stationary electric charges charges or repulsion between like charges
Directly proportional to the product of the
Matter has mass & energy equivalence. Matter charges
also may have electric charge! Inversely proportional to the square of the
distance between them
Electric Charge
Positive or negative Coulomb’s Law
It has potential energy The electrostatic force is directly
Smallest Units: electron & proton proportional to the product of the
Fundamental Unit (SI): coulomb (C) electrostatic charges & inversely
1 C: 6 x 1018 electron charges proportional to the square of the distance
between them
Electrified Formula: F = k(QaQb/d2)
The object that has too few or too many
electrons Electric charge distribution is uniform
throughout or on the surface!
Electrification
The process of adding or removing electrons Electric charge of a conductor is concentrated
from an object along the sharpest curvature of the surface!
It is created by contact, friction or by
induction Electric Potential
SI Unit: volt (V)
Electric Ground 1 V: 1 J/C or 1 potential energy/unit charge
The object that behaves as a reservoir for
stray electric charges ELECTRODYNAMICS
Electrostatic Laws Electrodynamics
Unlike charges attract The study of electric charges in motion
Like charge repel
Electric field radiate out from positive Electrical Engineer
charge Work with electric current
Electric field radiate toward a negative
charge Physicist
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Uncharged particles do not have electric Concerned with electron flow
field
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Four States of Matter
Electric Field Conductor, Insulator, Semiconductor,
The lines of force exerted on charged ions in Superconductor
the tissues by the electrodes
Conductor
STEWART C. BUSHONG SUMMARIZED BY: MEYNARD Y. CASTRO
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CHAPTER 5
ELECTRICITY, MAGNETISM, & ELECTROMAGNETISM
Any substance through which electrons flow The path of electron flow from the
easily generating source through the various
Characteristics: components & back again
o Variable resistance
o Obeys Ohm’s law Increasing electric resistance results in a
o Requires voltage reduced electric current!
Examples: copper (Z=29), aluminum (Z=13)
& water Electric Current/Electricity
The flow of electrons through a conductor
Insulator Direction: always opposite the electron flow
Any material that does not allow electron It is measured in Amperes (A)
flow 1 A: 1 C/s or 1 electric charge/second
Characteristics:
o Does not permit electron flow Electric Potential
o Extremely high resistance It is measured in volts (V)
o Necessary with high voltage 1 V: 1 J/C or 1 potential energy/unit charge
Examples: glass, rubber & clay
Electric Resistance
It is measured in ohms (Ω)
Semiconductor
A material that some conditions behaves as
Ohm’s Law
an insulator & as a conductor
The voltage across the total circuit or any
Characteristics:
portion of the circuit is equal to the current
o Can be conductive
times the resistance
o Can be resistive
Formulas: V = IR; R = V/I; I = V/R
o Basis for computers
Examples: silicon (Si-14) & germanium Two Basic Types of Electric Circuits
(Ge-32) Series & Parallel Circuits
Superconductor Series Circuit
Any material that allows electrons to flow All circuit elements are connected in a line
without resistance along the same conductor
Characteristics:
o No resistance to electron flow Rules for Series Circuit
o No electric potential required Rt = R 1 + R 2 + R 3
o Must be very cold It = I 1 = I 2 = I 3
Examples: niobium (Nb-41) & titanium (Ti- Vt = V 1 + V2 + V 3
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Parallel Circuit
William Shockley (1946) Elements are connected at their ends rather
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He demonstrated semiconduction than lying in a line along a conductor
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Superconductivity (1911)
The property of some matter to exhibit no
resistance below a critical temperature
Rules for Parallel Circuit
Electric Circuits It = I 1 + I 2 + I 3
STEWART C. BUSHONG SUMMARIZED BY: MEYNARD Y. CASTRO
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CHAPTER 5
ELECTRICITY, MAGNETISM, & ELECTROMAGNETISM
Vt = V 1 = V2 = V 3 Formulas: P = IV = I2R
1/Rt = 1/R1 + 1/R2 + 1/R3
MAGNETISM
SYMBOLS & FUNCTION OF ELECTRIC
CIRCUIT ELEMENTS Magnetite
Circuit Symbol Oxide of iron (Fe3O4)
Function Lodestone or leading stone
Elements
Inhibits flow of
Resistor Magnetism
electron
Provides electric The fundamental property of some forms of
Battery matter
potential
Momentarily It has no smallest unit
Capacitor stores electric
charge Any charged particle in motion creates a
Measures electric magnetic field!
Ammeter
voltage
Measures electric Electron Spin
Voltmeter A property created when electrons behave as
potential
Turns circuit on & if they rotate on its axis
Switch off by providing It is neutralized in electron pairs
infinite resistance It creates a magnetic field
Increases &
decreases voltage Magnetic Moment
Transformer A nuclear magnetic dipole created when
by fixed amount
(AC only) magnetic field is created by spinning electric
Rheostat Variable resistor charge
Allows electron to The basis of MRI
Diode flow only in one
direction The lines of a magnetic field are always closed
loop!
Direct Current
Electrons that flow in only one direction Dipolar/Bipolar
A magnet that has two poles
Alternating Current (AC) Poles: north & south pole
Electrons that flow alternately in opposite
direction Magnetic Dipole
60-Hz current The small magnet created by the electron
orbit
Waveform
The graphic representation of a wave Magnetic Domain
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x-axis: time An accumulation of many atomic magnets
y-axis: amplitude of electric current with their dipoles aligned
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AC: sinusoidal In Ferromagnetic Material: randomly
DC: straight line oriented
Electric Power
It is measured in watts (W) Magnetic Permeability
1 W: 1 A (current) x 1 V (voltage)
STEWART C. BUSHONG SUMMARIZED BY: MEYNARD Y. CASTRO
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CHAPTER 5
ELECTRICITY, MAGNETISM, & ELECTROMAGNETISM
The ability of a material to attract the lines
of magnetic field intensity Ferromagnetic
It can be strongly magnetized
Magnets are classified according to the origin of Example: alnico (Al-12, Ni-28, Co-27) &
the magnetic property! iron (Fe-26)
Three Principal Types of Magnets Magnetic Susceptibility
Naturally occurring magnets The degree to which a material can be
Artificially produced permanent magnets: magnetized
Electromagnets
Wood
Natural Magnet Low magnetic susceptibility
A magnet that gets its magnetism from the
Earth Iron
High magnetic susceptibility
Permanent Magnet
A magnet whose magnetism is induced Hysteresis
artificially A condition wherein some materials that are
A bar or horseshoe-shaped magnet very susceptible are also reluctant to lose
Example: compass their magnetism
Electromagnet Pole
A coil or wire wrapped around an iron core The magnetically charged end of a material
that intensifies the magnetic field North & south poles
All matters can be classified to the manner in Magnetic Laws
which it interacts with the external magnetic Like magnetic poles repel
field! Unlike magnetic poles attract
Imaginary lines of magnetic field leave the
Four Magnetic States of Matter north pole
Nonmagnetic, Diamagnetic, Paramagnetic, Imaginary lines of magnetic field enter the
& Ferromagnetic south pole
Nonmagnetic Magnetic Induction
Unaffected by magnetic field The process of making ferromagnetic
Example: wood & glass material magnetic
Diamagnetic Magnetic Lines of Induction
Weakly repelled from both poles of a The imaginary magnetic field lines
magnetic field
Example: copper, water & plastic
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Soft Iron
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An excellent temporary magnet
Paramagnetic
Weakly attracted to both poles of a magnetic Ferromagnetic objects can be made into magnets
field by induction!
Example: Gadolinium (Gd-64): contrast
agent in MRI
STEWART C. BUSHONG SUMMARIZED BY: MEYNARD Y. CASTRO
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CHAPTER 5
ELECTRICITY, MAGNETISM, & ELECTROMAGNETISM
Magnetic Force It determines the direction of the magnetic
The force of attraction between unlike poles field
or repulsion between like poles
Directly proportional to the product of the Solenoid
magnetic pole strengths A coil of wire
Inversely proportional to the square of the
distance between them Electromagnet
A current-carrying coil of wire wrapped
Magnetic Field Strength around an iron core
SI Unit: tesla (T) It intensifies the induced magnetic field
Older Unit: gauss (G) Advantage: magnetic field can be adjusted
1 T: 10,000 G or turned on & off
ELECTROMAGNETISM Electromagnetic Induction
An electric current is induced in a circuit if
Luigi Galvani (1700’s) some part of that circuit is in a changing
He observed that a dissected frog leg magnetic field
twitched when touched by two different e.g radio reception
metals
Michael Faraday
Alessandro Volta He observed the current in a changing
HE Contributed on the development of magnetic field
battery
Voltaic Pile: precursor of modern battery Faraday’s Law
o A copper-zinc plates like a Dagwood The first law of electromagnetic
sandwich
Modern Battery: carbon rod (+) & zinc FARADAY’S LAW
cylindrical can (-) The magnitude of the induced current depends
on four factors:
Source of Electromotive Force 1. The strength of magnetic field
Any device that converts some form of 2. The velocity of the magnetic field as it
energy directly into electric energy moves pass the conductor
3. The angle of the conductor to the magnetic
Ferromagnetic objects can be made into magnets field
by induction! 4. The number of turns in the conductor
Varying magnetic field intensity induces an
Hans Oersted (1820) electric current!
He demonstrated that electricity can be used
to generate magnetic fields Electromagnetic Devices
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Electric motor, Electric Generator &
Transformer
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Any charge in motion induces a magnetic field! Electric Motor
Electric current produces mechanical motion
Commutator Ring: switches the direction of
Right Hand Rule current through the loop
STEWART C. BUSHONG SUMMARIZED BY: MEYNARD Y. CASTRO
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CHAPTER 5
ELECTRICITY, MAGNETISM, & ELECTROMAGNETISM
Electric Generator A current that opposes the magnetic field
Mechanical motion produces electric current that induced it, creating a loss of transformer
efficiency
Transformer
It changes the intensity of alternating Autotransformer
voltage & current It consists of one winding of wire & varies
It works on AC only in voltage & current by self-induction
DC: induces no current in the secondary coil It is located in the operating console that
controls the kVp
Induction Motor
A type of motor used with x-rays tubes Shell-type Transformer
It powers the rotating anode of an x-ray tube It confines more of the magnet field lines of
the primary winding
Transformer Law Rationale: the secondary is wrapped around
The change in voltage is directly it & there are essentially two closed cores
proportional to the ratio of the number of Advantage: more efficient than closed-core
turns (windings) in the secondary coil (Ns) to transformer
the number of turns in the primary coil (Np)
Formula: Vs/Vp = Ns/Np
Step-up Transformer
Turns ratio greater than 1
Primary Side: low voltage, high current
Secondary Side: high voltage, low current
Step-down Transformer
Turns ratio less than 1
Primary Side: high voltage, low current
Secondary Side: low voltage, high current
Transformer Law Effect on Current
A change in current & a change in voltage
are inversely related
Formula: Is/Ip = Np/Ns = Vp/Vs
Types of Transformer
Closed-core, Autotransformer & Shell-type
Closed-core Transformer
A square core of ferromagnetic materials
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built up of laminated layers of iron
It helps to reduced energy losses caused by
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eddy current
Result: greater efficiency
Eddy Current
STEWART C. BUSHONG SUMMARIZED BY: MEYNARD Y. CASTRO
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