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80 Cards in this Set
- Front
- Back
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Electrical potential difference caused by movement of electrons from one material to another.
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Static electricity & electrical potential
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If electrons are moving from L to R what way is current moving?
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R to L
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Law describes the force between two charged particles
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Coulomb's Law
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Outer electrons or ions loosely bound and free to move? (copper wire)
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Conductors
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Electrons firmly bound. ELectrons don't escape from the wire
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Insulator
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Intermediate conductivity
Ex:thermistors, photodector |
Semiconductors
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Results from minute electric currents in material
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Magnetic field
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To determine a magnetic field strength you would use?
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Weber
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To determine magnetic density, you would use?
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Tesla
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The magnetic density produced in the air by the earths magnetic field?
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60uT
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Magnetic fields used by MRI equipment produce a magnetic flux density is in the range of?
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.2-4T
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Current flow of 1 Ampere is ?
(#) |
6.24 x 10 to the 18th electrons per sec(l)
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The interaction of an electric current and a magnetic field is the working principle of instruments such as the ?
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Galvanometer: measures current flow
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Steady flow of electrons along a wire or through a component in one direction only.
Ex: battery/ generator |
DC (direct current)
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Flow of electrons first in one direction and then in the opposite direction along a wire
Ex: what comes out of a wall |
AC (alternating current)
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Unit of current in the SI system
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Ampere
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That resistance which will allow 1 ampere of current to flow under the influence of an electrical potential of one volt
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Ohm
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Causes 1 amp of current to flow through a resistance of 1 ohm
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1 volt
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This law is the most important, basic law of electricity. It defines the relationship b/w the three fundamental electrical quantities: current, voltage, and resistance
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Ohm's Law
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Ohms law is the most imp. basic law of electricity. It defines the relationship b/w what three fundamental electical quantities?
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current, voltage, resistance
V= l x R |
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V1= 20 volts
R1= 50 Ohms if V= l x R find: l? |
l = V x R
20/50 = .4amperes =400mA |
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Power/Watts is = ?
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W= V x l
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This makes AC comparable to DC
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RMS voltage
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Stores electric charge in a circuit
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Capacitance (F)
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Provides resistance in an electrical circuit
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Resistors (Ohm)
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Increasing resistance
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resistors in series
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Decreasing resistance
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resistors in parallel
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The amount of electric charge accumulated by a 1 ampere current for 1 sec
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Coulomb
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changing magnetic fields induces what type of current flow in conductors?
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electrical current flow
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Changing electrical fields induces what materials?
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magnetism in ferrous materials
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Capacitance equal to coulombs per volt
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Farad (F)
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E= V x Q?
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Energy to move an electric charge Q through a potential difference V
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A measure of the ability of an object to hold an electric charge.
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Capacitance
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SI unit for charge
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Coulomb (C)
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The capacitance of an object for which the electrical potential increases by one V when one coulomb of charge is added
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Farad
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Farads or capacitance (F) = ?
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Charge or Coulombs/ Volts
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Unit of potential difference?
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Volt (V) or electomotive force (EMF)
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Process of generating electrical current in a conductor by placing the conductor in a changing magnetic field
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Induction or electromagnetic induction
(current is said to be induced in the conductor by the magnetic field) |
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Total opposition that a circuit presents to alternating current
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Electrical Impedance (Z)
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Inductor and impedance?
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the higher the frequency the higher the impedance
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Capacitor and impedance?
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the higher the frequency the lower the impedance
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Resistor and impedance?
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non-frequency dependent resistance
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Protects patient from low frequency AC current (the mains)by having a high impedance
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Isolating capacitor
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Semiconductor device which only permits current to flow in one direction
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Diode
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Leakage < 50uA with one fault
electrodes may contact heart directly Highest level of electrical safety |
TYPE CF: isolated circuit
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General monitoring circuits (isolated circuit)
Leakage < 500uA with one fault |
Type B or BF
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150uA capable of producing v FIB via intracardiac catheter
can be produced by <1 volt** Risk increases with low frequency AC Anesthetist can close path to ground from pt risk with: temporary internal pacemakers, esophageal stethoscope, external pacemakers |
Micro-Shock
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Pt susceptible to micro-shock
port cross sectional area very small contact with ventricular wall will not require much current to cause fibrillation |
Pulm. Artery Cath
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Converts the grounded power on the primary side to an ungrounded power system on the secondary side. Introduces a level of safety
Eliminates the potential of getting shocked through a ground |
Isolation transformer
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ESU
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Return pad
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Class I: all user accessible parts grounded
fuses present to disconnect live wire for excessive current flow |
3 prong plug
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Class II: all user accessible parts double insulated
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2 prong plug
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Class III: internally powered equipment
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batteries
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Takes shock through the pt without penetrating the skin
vascular access (catheters) myocardial lead wires |
Microshock
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Goes through the skin
intact skin |
Macroshock
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Commonly confused with pressure ischemia
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Burns
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When would you begin to feel effects of current?
(threshold of perception) |
1mA
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Accepted as maximum harmless current intensity
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5mA
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"Let-go" current before sustained muscle contraction
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10-20 mA
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Pain, possible fainting, mech. injury, heart and resp. functions continue
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50 mA
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VF will start, resp. center remains intact
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100mA
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100 uA
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VF (microshock)
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Greatest risk of serious shock with low frequency
Type of current we use |
60Hz
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What makes electrical currents passing through the body so dangerous?
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Path of current
current density frequency |
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Worst path of current?
Worst frequency is b/w? |
through the heart,BR,SC
frequency b/w 50-60Hz |
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Smaller/ larger area of contact more likely to get a significant burn?
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Smaller area
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J for external defib (max)?
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360J
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J for internal defib (max)?
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100J
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Capacitor blocks current flow after charging
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DC
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Capacitor allows current flow
May cause ECG interference in OR |
AC
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Prevented by shielding of wires and equipment
Generation of electrical signals in leads and monitoring equipment caused by EM field from other equipment |
Inductance and Interference
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Unwanted distortion of biological signals by capacitance and inductance effects
Cannot be eliminated by amplification Can be reduced by averaging repetitive waveforms |
Signal-to- Noise Ratio
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High frequency AC current minimizes risk of muscular contraction/ VF
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1 MHz
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Monopolar/Bipolar?used with forceps for coagulation
not to cut |
Bipolar
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Monopolar/Bipolar? used for cutting and coagulation
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Monopolar
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Typical defibrillator is at its maximum setting and potential of ?
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5000V (store of electrons equivalent to 160millicoulombs) of charge
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Energy= potential difference (V) x charge (Q)
what is the energy for a defibrillator if V= 160 and Q = 5000? |
1/2 x 160mC x 5000 V =
400 J |
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Current pulse/ discharge to produce synchronous contraction of myocardium followed by refractory period?
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35A for 3ms
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(defibrillator)
absorbs some of the delivered energy ensures that the electrical pulse has an optimum shape and duration |
Inductor
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(High)Desirable to increase measurement of biological potentials and reduce risk of electrocution
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Input impedance
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