Download Electricity and Magnetism

CVT 102
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Electron Theory
◦ All electronic effects caused by movement of
electrons
◦ Serves as basis for design of electrical equipment

Composed of protons, electrons, neutrons
◦ Nucleus
 positively charged protons
 neutral neutrons
 Negative charged electrons travel in orbits around nucleus
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Atomic Number
◦ Number of protons in the nucleus
◦ Determines characteristics of atom
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Mass Number
◦ Number of protons and neutrons in the nucleus
◦ On periodic table, given as average of commonly
occurring isotopes
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Electrons
◦ Revolve in shells or orbits
◦ Close to nucleus — strong attraction; outer orbits
— less attracted
◦ Free electrons located in outer orbits; movement
creates electric current

Electron Theory
◦ All electronic effects caused by movement of
electrons
◦ Serves as basis for design of electrical equipment

Atoms, Electrons, Matter
◦ Matter has mass and occupies space; consists of
atoms

Atoms, Electrons, Matter
◦ Atoms
 Composed of protons, electrons,
neutrons
 Nucleus is center; contains positive
charged protons and neutral charged
neutrons
 Negative charged electrons travel in
orbits around nucleus
 Atoms held together by opposite charges
of protons and electrons
 Different elements have varying numbers
of protons and electrons

Atoms, Electrons, Matter
◦ Electrons
 Revolve in shells or orbits
 Close to nucleus – strong attraction; outer orbits – less
attracted
 Free electrons located in outer orbits; movement
creates electric current
 Electricity: term actually describes movement of free
electrons moving from orbit of one atom to another
(principle based on Bohr’s Theory)

Atoms, Electrons, Matter
◦ Electrons con’t.
 A conductor is a material that allows flow of free
electrons
 The greater the number of electrons in a substance,
the better the conductor
 Copper is the most commonly used material for a
conductor. Silver, zinc and brass are also used.
 Devices in O.R. that use copper as a conductor:
surgical lamps, ESU, power drills
 Water is a conductor; humidity in O.R. should be
maintained at 50%-60%

Insulators
◦ Materials with small number of free electrons;
inhibit flow of electrons
◦ Basically poor conductors
◦ Used to wrap conductors to preserve current and
prevent leakage of electrons
◦ Types of insulators
 Rubber cord, plastic around ESU or X-ray machine

Electrical Charge
◦ Can be either positive or negative
◦ Defined as too many or too few electrons orbiting
an atom
◦ Law of Electric Charge: like charges repel each
other; unlike charges attract each other; opposites
attract

Electrical Current
◦ Movement of electrical charge
◦ Current moves through conductors by movement of
free electrons migrating from atom to atom inside
conductor

Magnetic Fields
◦ Electrons create a magnetic field or electric charge
while orbiting the nucleus
 In some materials electrons travel in the same
direction, combining magnetic fields
 Natural magnetic substances include iron, nickel,
cobalt, even the earth
◦ Electrical generators depend on the close
relationship of electricity and magnetism

Magnetic Fields con’t.
◦ Earth
 Two poles, north and south
 Magnetic field is lines of magnetic force between poles
 Magnetic field causes metal objects to be attracted to
the magnet; needle in a compass

Electromagnets
◦ Metals that become magnetic when encircled by a
conductor
◦ Magnetic field created by current traveling through
conductor
◦ Magnetic field used to create electricity
 Electricity does not create power; only means for
transporting it
◦ Interaction between wires and magnets produces
power

Electromagnets con’t.
◦ Example: Power plant
 Water from dam heated  forms steam  turns
turbines (generators)  turbines spin magnets 
electricity is created for use
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Terminology
Volt is electrical potential
– Voltage is potential energy of electrons
– Named after Alessandro Volta, a 17th
century scientist who invented the
battery
Electric system: battery creates voltage to
move electricity
Circuit is the path electricity travels
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Measured in amperes (amps)
Rate of flow of electrons
Current flow is the movement of free
electrons
Free electrons attracted from point of excess
electrons to a point with fewer electrons


Scientific law of electricity
– Mathematical equation showing how
voltage,
current, and resistance interrelate
– Ohm’s Law: V = I x R
Resistance
◦ Restricting flow of current; measured in ohms

Ohm’s Law
– More voltage will increase current if
resistance
is constant; higher resistance causes
decreased current if voltage is constant

Rate at which work is completed
◦ Rate of movement of electrons or current flow
◦ Product of voltage & current is power
◦ P=IxV

Measured in watts (W)
◦ Converted to kilowatts (KW): 1 KW = 1,000 W
◦ Example: DC Circuit is 12V & 20A, Power is
P = 20 x 12 = 240W or 0.24KW
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Device that uses electricity to perform a
function
Can change amount of energy from power
source
Examples: surgical lamps, ESU, power drills,
video monitors
Resistive energy loads: conductor has high
resistance to flow of electricity
◦ Example: filament (conductor) in light bulb;
electricity has to force way thru resistance to
cause filament to glow

Device used to open or close circuit
◦ Controls flow of electricity

Example: Flashlight
◦ Batteries (power)
◦ Wires (conductors) connected to battery that is
connected to switch activated by user
◦ Bulb (load) must have voltage
◦ Voltage carried by conductors and switch controls
flow of current to load; open switch – no flow,
closed switch bulb lights up

Hot Wire
◦ Wire that connects to switch; colored red

Neutral Wire
◦ Pathway for electrons to return to energy source;
complete the circuit; colored green

Ground Wire
◦ Sends leaking electrons to ground to prevent shock;
colored black


Devices made of materials that are purposely
resistive
Designated with letter R


Electrical current flows in one direction –
negative to positive pole
Example: Batteries
◦ Serve as storage device; keep electricity until
needed
◦ Negative (-) and positive (+) terminals
◦ When switch is closed, current flows from one
terminal to the other

Batteries con’t.
◦ Four components of DC circuit




Battery: source of electricity
Wire (battery to load): conductor
Switch: control device
Load: bulb
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Current that periodically reverses direction
Complete cycle is current that moves in one
direction, then reverses direction
Hertz (Hz): one AC cycle
Frequency: number of AC cycles in a second;
symbol ƒ
Most common AC in U.S. is 60 cycle AC
Typical voltage is 110V or 120V

AC Can Change Voltage
◦ AC delivered as high voltage, then “stepped down”
◦ Example:
 Transformers “step up” exiting voltage
 Power lines (transformer) deliver electricity at high
voltage
 Voltage is stepped down before use


Frequency is number of wave cycles (one
cycle is a hertz) per second
Radio and TV signals are electromagnetic
waves
◦ Radio transmitter delivers signal to antennae
system
◦ Electromagnetic signals travel through cable, air or
optical fiber to receiving antennae
◦ RF spectrum begins at 9 kHz (or less) to over 3 GHz


Cause of electrical shock
Secondary circuit contains hazardous current
due to isolated circuit
◦ Transformer insulation isolates secondary circuit
◦ Person touches both poles of non-insulated
isolated circuit and experiences an electrical shock
and/or burn

Secondary Circuit con’t.
◦ Two methods of prevention:
 Solid insulation placed as total barrier to prevent
complete access to circuit
 Conductive barrier of insulation between isolated
circuit and conductive barrier
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Application of electrical current through
tissue to coagulate bleeding or cut tissue
Electrosurgical Unit (ESU): Device that
provides power for electric current
Electrosurgery: Electrical currents applied
directly to tissue; utilizes AC current
Electrocautery: Uses heated wire to burn
tissue; no electricity enters body; utilizes DC
current
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ESU Circuit: Current Flow
◦ Generator  thru conductor cord  active electrode
(Bovie tip)  surgical site (energy converted to
thermal energy to cut or coagulate)  thru patient
 dispersive electrode (grounding pad) 
conductor cord  generator
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
Used for delicate procedures, presence of
moisture, prevent nerve damage
Two prongs of forceps: active and inactive
electrodes
◦ Current travels through one tip, passes thru tissue,
disperses to other tip

No dispersive electrode required
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Flow of current is as described in Slide 35
Dispersive Electrode (grounding pad)
◦ Placement is critical to avoid electrical burns to
patient
◦ Pad must be in complete contact with patient’s skin
◦ Pad pulled up or portion not in contact, may result
in second or third degree burns to patient

Shock and Burn
◦ Patient
 Burns usually deep; tissue necrosis; thrombosis
 Debridement
◦ Sterile Surgery Team Members
 RF Capacitive Coupling: AC travels from active
electrode, through intact insulation, burns skin; apply
active electrode beneath Crile held by surgeon to
prevent burns

Shock & Burn con’t.
◦ Sterile Surgery Team Members
 Dielectric Breakdown: High voltage breaks down
insulating material, such as sterile glove; produces
hole in glove – surgical team member sustains small
burn

Vaporized Tissue Plume
◦ Occurs during procedures involving electrosurgery,
lasers, power drills
◦ Plume is vaporized tissue
◦ Contains hazardous bioparticles that are
carcinogenic, mutagenic, and they may carriy
bloodborne pathogens
◦ Surgical technologists utilize suction to “suck
smoke” from wound when using electrosurgery or
smoke evacuators for lasers

Electricity
◦ Describes movement of free electrons moving from
orbit of one atom to another (principle based on
Bohr’s Theory)

Conductor
◦ material that allows flow of free electrons
◦ Copper is the most commonly used material for a
conductor. Silver, zinc and brass are also used.

Insulators
◦ Materials with small number of free electrons;
inhibit flow of electrons
◦ Basically poor conductors
◦ Used to wrap conductors to preserve current and
prevent leakage of electrons
◦ Types of insulators
 Rubber cord, plastic, paper

Electrical Charge
◦ Can be either positive or negative
◦ Charged is conserved
 Neutral objects contain equal numbers of positive and
negative charges
◦ Like charges repel; unlike charges attract

The force (attraction or repulsion) between
two charged particles is proportional to the
product of their charges and inversely
proportional to the square of the distance
between them. (Inverse square law)
 SI
unit
◦ Coulomb (C)
 6.25 X 1018 electrons
 Very large amount of charge
 Coulomb force between two charges of 1 .0 C
each separated by 1 .0 m is 9X109 N (about 1
million tons)


Charges on surface of object
Charge is greater on curved surface; greater
the curvature, the greater the charge
 Click here for more information about static electricity

Electrical Current
◦ Movement of electrical charge
◦ Current moves through conductors by movement of
free electrons migrating from atom to atom inside
conductor

Magnetic Fields
◦ Electrons create a magnetic field or electric charge
while orbiting the nucleus
◦ In some materials electrons travel in the same
direction, combining magnetic fields
◦ Natural magnetic substances include iron, nickel,
cobalt, even the earth

Magnetic Fields
◦ Earth
 Two poles, north and south
 Magnetic field is lines of magnetic force
between poles
 Magnetic field causes metal objects to be
attracted to the magnet; needle in a
compass

• Electromagnets
◦ Metals that become magnetic when encircled by a
conductor with an electric current
◦ Magnetic field created by current traveling through
conductor


Electrical generators depend on the close
relationship of electricity and magnetism
Magnetic field used to create electricity
◦ Interaction between wires and magnets produces
electricity

Example: Power plant
• Water from dam heated —* forms steam —
* turns turbines (generators) —* turbines spin
magnets —* electricity is created for use

Volts
◦ Volt is electrical potential
◦ Voltage is potential energy of electrons
◦ Named after Alessandro Volta, a 17th
century scientist who invented the battery


Electric system: battery creates voltage to
move electricity
Circuit is the path electricity travels



Measured in amperes (amps)
Rate of flow of electrons
Current flow is the movement of free
electrons
◦ Free electrons attracted from point of excess
electrons to a point with fewer electrons


Device that uses electricity to perform a function
Can change amount of energy from power source
◦ Examples: lights, ESU, power drills, video monitors
◦ Resistive energy loads: conductor has high resistance to
flow of electricity
 Example: filament (conductor) in light bulb; electricity has to
force way thru resistance to cause filament to glow

Measured in Ohms (Ώ)


Mathematical equation showing how voltage,
current, and resistance interrelate
Ohm’s Law:
V=IxR
◦ More voltage will increase current if resistance is
constant
◦ Higher resistance causes decreased current if
voltage is constant

Rate at which work is completed
Rate of movement of electrons or current flow
Product of voltage & current is power

P=IxV



Measured in watts (W)
o Converted to kilowatts (KW): 1 KW =
1,000 W
o Example: DC Circuit is 12V & 20A, Power
is
o P=20x12=24OWorO.24KW

Device used to open or close circuit
◦ Controls flow of electricity
 Example: Flashlight
 Batteries (power)
 Wires (conductors) connected to battery that is connected
to switch activated by user
 Bulb (load) must have voltage
 Voltage carried by conductors and switch controls flow of
current to load
 open switch — no flow
 closed switch bulb lights up

Hot Wire
◦ Wire that connects to switch; colored red

Neutral Wire
◦ Pathway for electrons to return to energy source;
complete the circuit; colored green

Ground Wire
◦ Sends leaking electrons to ground to prevent shock;
colored black

Electrical current flows in one direction —
negative to positive pole
◦ Example: Battery
 Serves as storage device; keep electricity until
needed
 Negative (-) and positive (+) terminals
 When switch is closed, current flows from one
terminal to the other

Four components of DC circuit
◦
◦
◦
◦
Battery: source of electricity
Wire (battery to load): conductor
Switch: control device
Load: bulb


Current that periodically reverses direction
Complete cycle is current that moves in one
direction, then reverses direction
◦ Hertz (Hz): one AC cycle
◦ Frequency: number of AC cycles in a second;
symbol f
◦ Most common AC in U.S. is 60 cycle AC
◦ Typical voltage is 110V or 120V



AC voltage can be changed by transformer
AC delivered as high voltage, then “stepped down”
Example
◦ Transformers “step up” exiting voltage
◦ Power lines (transformer) deliver electricity at high voltage
◦ Voltage is stepped down before use



Fuses
Circuit breakers
Ground
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Mutual induction
The transformer equation relates the number
of turns of wire to the difference in voltage
between the primary and secondary coils.
 Vp/Vs
=
Np/
Ns
◦ Where Vp is the voltage in the primary coil.
Vs is the voltage in the secondary coil.
Np is the number of turns of wire on the primary coil.
Ns is the number of turns of wire on the secondary coil.
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Step-up transformer
Click on the image above for more information
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Step-down transformer
Click on the image above for more information