12 Electricity Flashcards
Current
Electron flow (I) How much charge (how many electrons) pass through certain point in circuit per unit time Quantity measured in Amperes Body current = ion movement
Capacitance
Stored charge
Substance ability to store a charge
Inductance
How electricity generated
Ohm’s Law
I = V / R
Analogous to Q = ΔP/R or BP = CO x SVR
Voltage
Electromotive force (EMF) or force that pushes electrons through resistance
Electrical charge potential difference directly proportional to electron flow (electric current)
Driving pressure P1 - P2
Measured in Volts
Resistance
Opposition force to electron flow
Flow inversely proportional to resistance
Measured in Ohms
Coulomb
Electric charge measure unit
1e¯ = 1.602 x 10^-19
1 Coulomb = 6.24 x 10^18 electrons
1 Coulomb e¯/sec = 1 Amp
Ampere
Ampere (Amp) measures current
1 Amp = charge movement carried by 6.24 x 10^18 electrons passing a certain point in 1 second
1 Amp = 1 Coulomb electric charge movement
I = V / R
Current = voltage/resistance E = I x R Electromotive force (E) = voltage E = I x Z Impedance (Z)
Impedance
Represented by Z
Resistance to current flow that changes w/ frequency
Power supply frequency at constant 60Hz
Impedance & resistance are interchangeable
High impedance = low current flow
Low impedance = high current flow
Watt
Power unit (work/time)
Joules/second
Electrical power measurement
W = V x I
Joule
Watt-second = work = energy
Work = mass x acceleration x distance
kg x m/s^2 x m or 1 Joule
Work
Force x distance (displacement)
Force = mass x acceleration
Measured in Joules
Energy
Kinetic = (mass x velocity^2) / 2 Potential = mass x 9.81m/s^2 x height
Power
Measured as Watts in electrical circuit
I x V
Conductor
Permits e¯ flow
Current = e¯ flow through conductor
Non-Conductors
Insulators
Tightly bound electrons that do not permit e¯ flow
Ex: glass, rubber, plastic, dry wood, pure water
DC
Direct current
e¯ flow always in the same direction
Ex: batteries
AC
Alternating current
e¯ flow reverses direction (oscillates) at regular intervals
Oscillating frequency measured in cycles per second (Hertz or Hz)
Ex: electric company
Capacitance
Substance ability to store a charge
Capacitor
Electrical device used to shore electric charge
Basic design - 2 parallel conducting plates separated by insulating layer called dielectric
Electromagnetic Field
Force field that consists both electric & magnetic components
Resulting from electric charge motion & containing definite amount electromagnetic energy
Electrons flow through wire induce a magnetic field around
When wire coiled repeatedly around an iron core → amplifies the magnetic field
Dual nature r/t electricity & magnetism
- Where there’s an electric current there are also magnetic waves
- Where there are changing magnetic waves there’s an electric current
Able to do work
Inductance
e¯ flow via wire induce magnetic field surrounding
When wire coiled repeatedly around an iron core this will increase the electromagnetic field to move e¯
Ex: wireless charging
Motor
Battery source
Metal bar w/ coiled wire
Fixed magnets
Opposing magnetic fields repel e¯ to rotate the metal bar
Generator
No power source
Fixed metal bar w/ coiled wire
EMF moves around wire → inductance
Magnets rotate to power light bulb
“Hot” Conductor
Carries the current through the impedance
“Neutral” Conductor
Return the current to the source
Shock Hazards
Contact external electricity source
AC or DC current
Source - when person becomes part or completes an electric circuit; must contact the electric circuit at 2 points and there must be voltage source causing current to flow
Electricity Damage
Current disrupts normal cell electrical function
Or current passing through resistance (body) increases the temperature and can produce a burn
Severity depends on amount of current (Amperes) & contact duration
Macroshock
Large amount current
100-300mA V fib
Microshock
Very small amount current
External conductor in direct contact w/ the heart
PA catheter filled w/ NS
100μA (0.1mA) V fib
10μA (0.01mA)
Patient protected by intact ground wire to prevent microshock
Equipment ground wire broken all leakage current able to flow through the catheter → V fib
Grounding
Operating room NOT grounded Equipment = grounded Grounded 1° electrical company supply No direct contact b/w power supply & secondary side OR isolated power supply
Line Isolation Monitor (LIM)
Continuously checks line 1 & 2 for any current to ground
Any current between line 1 & ground OR line 2 & ground = short circuit
There should be no current b/w line 1 or 2 & ground
Able to used device, but need to replace when possible
Alarm indicates that system no longer totally isolated from ground → short
2mA in older LIM models
5mA in newer LIMs
Electrosurgical Units
ESU or Bovie
High frequency AC currents
500,000 up to 1 million Hz
Produces up to 3,000V & 400W
Heat generated when current passes through resistance
H = I^2 / A
Heat = current^2 / surface area
Small surface area increases heat to cauterize, cut, & seal off blood vessels
High frequency currents have low tissue penetration & do not excite contractile cells therefore do no cause V fib
Return Plate
Dispersive electrode w/ large surface area to complete the circuit
Collects & returns energy from the ESU/Bovie
Energy passes through the patient to return place and routed back to the ESU
Large surface area to prevent burns
Return Plate Placement
Close to operative site
Away from EKG pads
Ensure adequate gel & sufficient skin contact
Do not place over scar tissue, hair, or implants (these prevent good contact w/ the skin and decrease area)
Unipolar
Current returns to unit via dispersive pad
Bipolar
Two electrodes - look like forceps
Active & collecting electrode
Collecting completes the circuit back to source
No dispersive pad needed
Less energy than unipolar (just b/w the 2 electrodes)
Anesthesia Concerns
Radiofrequency waves interfere w/ monitors
ESUs able to reprogram demand pacemakers or cause microshock
Prepare to treat potential dysrhythmias
Inspect return place to ensure applied properly & effective conduction
Disable AICD (automatic implantable cardioverter defibrillator) prior to surgery by placing magnet over
