Electricity, Magnetism, and Electromagnetism
Friction
X-ray Imaging System ● build up of electron by rubbing objects
● to convert electric energy into together
electromagnetic energy
Induction
Electrostatics ● using the electric field of a charged object to
● study of stationary electric charge confer a charge on an uncharged object
Electric Charge Contact
● positive or negative ● a connection that causes the flow of electron
Smallest Units : Proton and Electron Electric Ground
● earth serves as a huge reservoir for stray
Electron electric charges
● has one unit of negative charge
Proton Electrostatic Law
● has one unit of positive charge 1. Unlike charges attract; like charges repel
● associated with each electric charge is an
Coulomb (C) - 6.3 x 10^18 electron charges electric field wherein neutron do not have an
Electrostatic Charge of Electron : 1.6 x 10^19 C/ electric field
electron charges ● the force of attraction between unlike charges
or repulsion is called electrostatic force due to
Electron Charge and Electric Forces the electric field
● electrons are free to travel from the outermost 2. The additional or removal of electron is called
shell of one atom to another electrification
● protons are fixed inside the nucleus of an 3. Only negative charge can move in solids
atom and are not free to travel 4. Coulomb's Law
5. When an object becomes electrified, the
Ions electrical charges are distributed throughout
● atom with net electric charge the object
● ordinary atoms are neutral because there is a 6. Electrical charge of a conductor is
balance between the number of protons and concentrated along the sharpest curvature of
electrons the surface
Electric Charge and Electric Forces Electric Potential or Voltage
● electrons move from atom to another thus ● a system that possesses potential energy is a
creating ions system with stored energy
● the higher the voltage, the greater the
Electrified potential to do work
● as object is said to be electrified if it has too ● x-ray imaging system : 220 V or higher
few or too many electrons ● 1 V = 1 J/C
Electrification Electrodynamics
● occurs when an object is or becomes ● study of charges in motion
charged by the removal or addition of
electrons
Electricity / Electric Current
● happens when an electric potential is applied Ohm’s Law
to objects such as copper wire then electrons ● V (volts) = IR
move along the wire ● I (ampere) = V/R
● R (ohms) = V/I
Four Electrical States of Matter
1. Conductors 2 Types of Electric Circuit
● allow electrons to flow easily 1. Series Circuit
● variable resistance, obey ohm’s law, required ● all components are connected in a line along
voltage the same conductor
● the components are lined up along one path
2. Insulator ● if the circuit is broken, all components turns
● inhibits the flow of electrons off
● does not permit electron to flow, extremely
high resistance, necessary with high voltage 2. Parallel Circuit
● contains elements that are connected at their
3. Semiconductors (William Shockley in 1946) ends rather than lying on a line along a
● a material that under some conditions conductor
behaves as an insulator and as a conductor ● if one branch of the circuit is broken, only the
● can be conductive or resistive, basis for components on that branch will turn off
computer technology
Series Circuit
4. Superconductivity
● property of some materials to exhibit no RT = R1 + R2 + R3
resistance below a critical temperature
● no resistance to electron flow, no electric IT = I1 = I2 = I3
potential required, does not obey the ohm’s VT = V1 + V2 + V3
law, must be very cold
Parallel Circuit
Electric Circuit
● the result when the resistance is controlled IT = I1 + I2 + I3
and the conductor is made into a closed path VT = V1 + V2 + V3
Ampere (A) I/RT = I/R1 + I/R2 + I/R3
● it measures the number of electrons flowing
in the electric circuit Electric Current/Electricity
● 1 A = 1 C/s ● flow of electrons through a conductor
Resistance 1. Direct Current
● opposition to the flow of an electric current, ● graph : horizontal/flat line
producing heat ● electrons flow in one direction along the
● resistance and current is inversely conductor
proportional ● where electrons flow in the same direction in
● good conductors have low resistance a wire
Factors that influence resistance
● material, thickness/cross sectional diameter
(inversely proportional to the resistance),
length, and temperature
2. Alternating Current therefore atoms that have an odd number of
● graph : sine wave electrons in any shell exhibits a very small
● electrons oscillates back and forth, swing magnetic field
from + to - side
● Electrons flow in different direction in a wire Magnetic Moment
● Spinning electric charges also induce a
Electric Power magnetic field, basis of MRI
● units : watts (W) = 1A
● P = IV = IR = I2R Magnetic Dipole
● small magnet created by the electron orbit
Magnetism
● the properties and interactions of magnets Magnetic Domain
● created by the accumulation of many atomic
History of Magnetism magnets with their dipoles aligned
● around 1000 BC, shepherds and dairy ● if all the magnetic domains in an object are
farmers near the village of Magnesia aligned, it acts like a magnet
(Western Turkey) discovered Magnetite, an
oxide of iron Magnetic Permeability
● this rodlike stone, when suspended by a ● ability of a material to attract lines of a
string, would rotate back and forth, when it magnetic field intensity
came to rest, it pointed the way to water,
called lodestone or leading stone Magnetic Susceptibility
● any charged particle in motion creates a ● the degree to which a material can be
magnetic field magnetized
Introduction to Magnetism Hysteresis Loss/Lagging Loss
● magnets have two ends or poles, north and ● “shortcoming”
south pole ● a loss in the core of transformer that occurs
● at the poles of a magnet, the magnetic field because demagnetization leaves some
lines are closer together dipoles
● the imaginary loans of a magnetic field are ● very susceptible material are reluctant to lose
always closed loops their magnetism
● the lines of a magnetic field do not start or
end as the lines of an electric field do Classification of Magnets
(according to the origin of the magnetic properties)
Magnetic Field 1. Naturally Occurring Magnets
● a magnet that is moved in space near a ● examples are earth and lodestone
second magnet experiences a magnetic field
● represented by field lines 2. Artificially Induced Permanent Magnets
● the strength of the magnetic field is greater ● permanent magnets are typically produced by
where the lines are closer together and aligning their domains in the field of an
weaker when farther apart electromagnet
● despite its name, permanent magnets, they
Electron Spin do not necessarily stay permanent
● electrons behave as if they rotate on an axis ● the magnetic property of a magnet can be
clockwise or counterclockwise that creates a destroyed by : heating it or hitting it with a
property called electron spin hammer which causes a disruption in the
● the electron spin creates a magnetic field, alignment of magnetic domain
which is neutralized in electron pairs
3. Electromagnets
● consists of wire wrapped around an iron core 3. Magnetic Induction
● purpose of iron core : to increase the intensity ● just an electrostatic charge can be induced
of the magnetic field from one material to another, so too same
● solenoid : coil of wire materials can be made magnetic by induction
● when an electric current is conducted through ● ferromagnetic material can be made
the wire, a magnetic field is created magnetic by being placed in the magnetic
● the intensity of the magnetic field is field lines of a magnet
proportional to the electric current ● the imaginary magnetic field lines just
● the magnetic field of a solenoid is described are called magnetic lines of
concentrated in the center of the coil induction
● the density of these lines is proportional to
the intensity of the magnetic field
Four Magnetic States of Matter ● soft iron : excellent temporary magnet
1. Nonmagnetic ● magnet only while its magnetism is induced
● unaffected when brought into a magnetic field
● examples include wood and glass 4. Magnetic Force or Maxwell Field Theory
(Gauss Law)
2. Ferromagnetic
● strongly attracted by a magnet, can be ● the magnetic force is proportional to the
permanently magnetized by exposure to a product of the magnetic pole strengths
magnetic field divided by the square of the distance
● examples : Fe -26, Al-13, Ni-28, Co-27, and between them
rare earth ceramics ● this magnetic force is similar to electrostatic
and gravitational force that also are inversely
3. Paramagnetic proportional to the square of the distance
● material lies somewhere between between the objects under consideration
ferromagnetic and nonmagnetic ● if the distance between two bar is halved the
● slightly attracted to a magnet and are loosely magnetic force increases by four times
influenced by an external magnetic field ● SI Unit of Magnetic Field Strength : Tesla
● examples : gadolinium - contrast for MRI ● Older Unit : Gauss
● 1T = 10,000 G
4. Diamagnetic
● materials are weakly repelled by either Earth’s Magnetic Field
magnetic pole ● equator = 50 uT
● cannot be artificially magnetized, and they ● poles = 100 uT
are not attracted to magnets
● examples : water, plastic, Cu-29 Electromagnetism
● until the 19th century, electricity and
Magnetic Laws magnetism were viewed as separate effects
1. Magnetic Dipoles
● every magnet, no matter how small has two Luigi Galvani (1700s)
poles ● an Italian Anatomist, observed two different
● north and south poles, equivalent to positive metals, just as if it had been touched by an
and negative electrostatic charges electrostatic charge
2. Attraction and Repulsion
● similar to electrostatic charges, like magnetic
poles repel and unlike magnetic poles attract
Alessandro Volta ● the magnetic field produced by an
● an Italian Physicist, investigate whether an electromagnet is the same as that produced
electric current might be produced when two by a bar magnet
different metals are brought into contact ● the advantage of the electromagnet is that its
● using zinc and copper (ZiCu) plates, Volta magnetic field can be adjusted by varying the
succeeded in producing a feeble electric current through its coil of wire
current
● to increase the current, he stacked the ZiCu Electromagnetic Induction
plates like a dagwood sandwich to form what
was called the Voltaic Pile Faraday’s Law
● voltaic pile - precursor of the modern battery ● faraday concluded that an electric current
● each ZiCu sandwich is called a cell of the cannot be induced in a circuit merely by the
battery presence of a magnetic field
● modern dry cells use a carbon rod as the ● in his experiment, a coil of wire is connected
positive electrode surrounded by an to a current-measuring device called an
electrolytic paste housed in a negative zinc ammeter
cylindrical can ● if a bar magnet were set next to the coil, the
meter would indicate no current in the coil
Battery ● he discovered that when the magnet is
● is an example of electromotive force moved, the coiled wire does have a current,
● any device that converts some form of energy as indicated by the ammeter
directly into electric energy is said to be a ● to induce a current with the use of a magnetic
source of electric potential field, the magnetic field cannot be constant
● electrical potential : J/C or V but must be changing
● no physical motion is needed
Hans Oersted ● an electromagnet can be fixed near a coil of
● a Danish Physicist, discovered the first like wire
between electric and magnetism ● if the current in the electromagnet is then
● with no current in the wire, the magnetic increased or decreased, the magnetic field
compass pointed north will likewise change and induce a current in
● when a current was passed through the wire, the coil
the compass swung to point straight at the
wire Electromagnetic Induction
● demonstrated that electricity can be used to ● an electric current is induced in a circuit if
generate magnetic phenomena some part of that circuit is in a changing
magnetic field
Electromagnetism
● any charged particle in motion induces a 2 Types of Induction
magnetic field 1. Self Induction
● a charge at rest produces no magnetic field ● the induction of an opposing magnetic
thus electrons flowing through the wire electromagnetic field in a single coil by its
produce a magnetic field around the wire own changing electric current
Electromagnet 2. Mutual Induction
● is a current carrying a coil the wire wrapped ● the process of inducing a current flow through
around an iron core, which intensifies the a secondary coil passing a varying current
induced magnetic field through the primary coil
● the magnitude of the induced current
depends on four factors : (1) the strength of
the MF, (2) the velocity of the MF as it moves Secondary Coil
past the conductor, (3) the angle of the ● supplied/output
conductor to the MF, (4) the number of turns ● current is induced
Lenz Law Types of Transformers
● 1834, a Russian Scientist, Heinrich Lenz ● closed-core transformer
expanded on Faraday’s work ● square core of ferromagnetic material
● he established the principle for determining ● the ferromagnetic core is not a single piece
the direction induced current flow but rather is built out of laminated layers of
● states that the induced current flows in a iron
direction that opposes the action that induces ● this layering helps reduce energy losses,
it resulting in greater efficiency
Autotransformer
● small step-up or step down transformer
● not suitable for use as the high voltage
transformer in an x-ray imaging system
Electromechanical and Electronic Devices ● variable transformer, consist of an iron core
1. Electric Generator (Faraday) with only one winding of wire that acts both
● convert mechanical to electrical energy the primary and secondary windings
● smaller compared to other transformer works
2. Electric Motor (Oersted) on principle of self-induction
● convert electrical to mechanical energy
Shell-type Transformer
3. Transformer ● confines even more of the magnetic field lines
● changes the intensity of alternating voltage of the primary winding because the
and current secondary is wrapped around it and there are
● does not convert one form of energy to essentially two closed cores
another, only transforms electric potential and ● most currently used, more efficient than
current into higher or lower intensity closed core transformer
● operates on the principle of mutual induction,
it will only operate with a changing electric
current
● a direct current applied to the primary coil will
induce no current in the secondary coil
● the voltage change across the transformer is
proportional to the turns ratio
Step-up Transformer
● turns ratio greater than 1
● the voltage is increased or stepped up from 4. Rectifiers
the primary side to the secondary side ● changes AC to DC
● Difference between AC and DC: commutator
Step-down Transformer ring
● turns ratio less than 1 ● AC - slip ring
● DC - split ring
Primary Coil ● types of Rectifiers : vacuum tube and solid
● receiver/input state rectifiers
● supplied with current
