Flashcards in Electricity Deck (57):
What is electricity?
The effects produced by moving charges
What is an electric force?
A non-contact force by a charged object exerted upon other objects (both charged and uncharged)
What are the charges like with protons and electrons?
Electrons: - 1.6 X 10^-19 Coulombs
Protons: 1.6 x 10^-19 Coulombs
What is the fundamental principle of charge interaction?
A positively charged object will attract a negatively charged object
- like charges oppose each other
- the magnitude of the electrostatic force is given by Coulomb’s law
If we put a “test charge” into an electric field, it feels forces resulting from _____________ __________.
What is an electric current?
Amount of energy flowing per unit of time
1 ampere (amp)= 1 Coulomb/second
What are conductors?
Materials in which charges can easily move (metals are good conductors)
—> to be a good conductor, electrons must be able to move easily from 1 atom to the next
What are insulators?
Not good conductors-hold on to their electrons
Usually non-metals, except for graphite
What is special about conductors?
Made of atoms that do not hold electrons tightly
- metals make good conductors because they have electron shells that are mostly empty
What are molecular orbitals?
Individual orbitals are added together to form molecular orbitals that extend over the entire molecule
—> typically result in a band of orbitals that is o nay partially filled-has room to accept new electrons with very little energy
How does copper act as a conductor?
Copper’s valence electrons move freely about the solid copper metal —> when influenced by external electrons, the outer shell electrons are repulsed and move away, repulsing other electrons and moving them along the wire
What is resistance and how is it measured?
- energy required to push electrons through a material
- measure in Ohms
(Electron repulsion is resistance, in the body blood and blood vessels are the resistance)
What is Ohms Law?
Where V = I x R
What is conductance like in relation to resistance?
Conductance is the reciprocal of resistance
Measured in mhos or Siemens
What is an electric circuit?
Closed path through which a charge flows
What is direct current (DC)?
Electric current in which the current only flow in 1 direction
- cannot transfer over a long distance
- electron flow in always in the same direction
What is alternating current (AC)?
Electric current in which the current reverses direction in a periodic fashion—> electron flow reverses itself at regular intervals
What is a short circuit and what is the risk?
A situation in a circuit where the normal resistance of the circuit is bypassed by a low resistance path, resulting in a large current
- if current is not limited by a fuse or circuit breaker, the heat could cause a fire
What happens when batteries or resistors are connected in series?
Voltages and resistances are added directly
What happens when resistors are connected in parallel?
Current flows through each resistor independently of the others
- allows for unique flow through each resistor (household appliances)
* in parallel resistances are added inversely *
1/R total= 1/R1 + 1/R2
What is electrical power?
The product of volts and amps—> measured in watts
Power= rate of using energy or
Power = energy/time
Energy = power x time
What do you pay for each month, energy or power?
What is a semiconductor?
- materials with electrical conducting properties between insulators and conductors
- impurities are added (aka doping) to more precisely control the properties of the material
- silicon is used as a semiconductor base
What is a P type semiconductor?
- group IV material (silicon) doped with a group III material (boron) that has 1 less valence electron than silicon
- the crystalline lattice thinks it is a few electrons short or has ”positive holes”
What is an N type semiconductor?
- silicon (group IV) is doped with something like arsenic (group V), which has 1 more electron than silicon
- the crystalline lattice thinks it has extra electrons
What are diodes?
Have large conductance in 1 direction and smaller in reverse to control the direction of the current
- P and N types are placed next to each other to make this happen
What is the junction between the p and n type semiconductors called?
What is forward bias?
A voltage is applied to the diode so that the n-region is biased negative related to the p-region
How do light emitting diodes (LEDs) work?
- voltage is applied to n-type region and moves toward p type region (forward bias)
- if DC maintained, holes and electrons will move toward the pn-junction an annihilate
- annihilation is exothermic, releasing energy as a photon of light
What is reverse bias?
Reverse polarity of DC power supply
- holes and electrons migrate away from PN-junction creating a depletion region
* high resistance *
- used only i f you need a small amount of current, helps you control energy passing through it
- direction of little or no current flow
What are triodes (transistors)?
- used to amplify or switch currents
- has forward and reverse bias
What is macroshock?
Large amounts of current conducted through patient’s skin or other tissues
- extent of injury depends on amount of current and duration of exposure
What is microshock?
Delivery of small amounts of current directly to the heart
* very small current (<50nA) can produce v-fib
T/F. V-fib can be produced by a current that is below the threshold of human perception?
- stray capitance from any AC powered electrical instrument may result in significant amount of charge build up on the case of the instrument
What part of equipment provides a low resistance pathway for current leakage and is the major source of protection from microshock in a patient?
What are some safety features to prevent shock?
- 3 pronged grounded plug: 3rd prong wired directly to casing of electrical device
- if high potential wire comes into contact with case—> current flows through 3rd prong instead of your body
- Polarized plugs: 1 narrow prong (high potential), 1 wide prong (low potential) - plug has 1 narrow slot and 1 wide so can only plug in one way
- Ground Fault Circuit Interrupter (GFCI):
- used near water sources
- immediately (within 1 ms) distrusts flow of current in circuit if a change in current is detected
- path of least resistance—> circuit moves faster- ground fault senses this and shuts off electric flow (can also have 3 prong plug with this)
What is a disadvantage of GFCIs in the OR?
- interrupts owner without warning—> defective equipment can no longer be used
- this is a problem if life support equipment shuts off
Are GFCIs used in the OR?
What puts humans at risk with grounded systems?
- what they are touching—> have to only touch a single object to complete a circuit, resulting in a shock
In the OR, how are electrical systems isolated from the grounded electrical supply?
How does an isolation transformer work?
Magnetic inductance transfers a current from grounded electrical system to an ungrounded secondary system
- the 2 systems never physically contact each other
- prevents accidental shocks from touching a single live wire
(Would need to touch both wires to get shocked)
—> one from each system
What is a line isolation monitor and how does it work?
Device that alarms when a fault in an ungrounded system occurs
- if live wires make contact with a ground, the ungrounded system now becomes grounded (fault)
- the alarm lets you know a fault has occurred
- system is now grounded—> a 2nd fault will result in a shock
Where are the line isolation monitors located?
- between live wires and a ground so that impedance can be measured
- if contact made between live wire and a ground, current will flow—> alarm sounds
What is the alarm set point for a line iso. Monitor?
If a line isolation monitor alarms, how do you determine if it is a true fault?
- if gauge reads 2-5 mA—> there’s probably too much electrical equipment plugged into circuit
** if gauge reads >5mA—> likely there’s a faulty piece of equipment present
—> unplug each piece of equipment until alarm stops—> if equipment non-essential, remove it
Does the line isolation monitor protect from microshock?
Monitors high voltage system—> macroshock only
How does the NFPA decide if isolated power should be installed?
1.) is the room wet?
2.) is an interruptible power supply acceptable?
T/F the NFPA no longer requires isolation power systems, or line isolation monitors in areas designated for use of o not non-flammable anesthetics.
Are all health care facilities required to have emergency source of power?
What is the objective of electrical safety?
Make it difficult form electrical current to pass through people
Where should power cords be located?
Overhead or areas of low traffic
- not on the floor
- extension circuits should not be on floor either, where they can come in contact with electrolyte solutions
How does electrosurgery work?
- high frequency currents are generated (radio frequency range)
- heat generated when a current passes through high resistance
What is true regarding high frequency currents?
- have low tissue penetration
- do to excite contractile cells
- energy generated by electrosurgery interferes with signals form physiologic monitors
In electrosurgery it is essential for energy to be routed from the unit through the patient and back to the unit via a _______________________________.
Large surface area dispersive electrode
Aka a return plate
If return plate cord is broken, what will happen?
Then high frequency electric current will seek an alternative path—> the patient or others
What is the most important factor in preventing patient burns from the ESU (electrosurgery unit)?
Proper application of the return plate
- don’t try to put this on, have someone who has been trained it in apply it