CVT 102

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

Atomic Number◦ Number of protons in the nucleus◦ Determines characteristics of atom

Mass Number◦ Number of protons and neutrons in the nucleus◦ On periodic table, given as average of commonly

occurring isotopes

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

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

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 = I x V

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

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

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

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

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

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

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

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.

Step-up transformer

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Step-down transformer

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