Electricity Flashcards
in electricity, current is
the movement of electrons
electric current
how much charge (how many electrons) pass a certain point in a circuit per unit time
each electron has a charge of
1.60217733 x10^-19 coulombs
a coulomb
unit of measure of electric charge
6.24 x10^18 electrons carry charge of
1 coulomb
movement of 1 coulomb of charge in 1 second is
1 ampere (amp)
1 amp of current =
1 coulomb/sec
the flow of electrons (electric current) is inversely proportional to
resistance
electromotive force
potential difference of electric charges from one area to the next
(pushes the electrons through the resistance)
the greater the potential difference
the greater the push of electrons through a resistance and the greater the flow of electrons
potential difference is directly proportional to
the flow of electrons (electric current)
equation for the relation of flow of electrons, potential difference, and resistance
I = V/R I = current, V = voltage, R = resistance
the potential difference is measured in
Volts
current is quantity of electrons measured in
amperes (amps)
resistance is measured in
Ohms
current can only flow if it gets
pushed
2 forms of electrical current flow thru a conductor
alternating current (Volts-AC) direct current (Volts-DC)
Impedance
Z
consist of resistance plus other factors that effect electron flow
examples of EMF
static electricity, lightening
the product of voltage and current
watt (unit of power)
amount of electrical work done measured in
watt-sec which = joules
energy produced by defibrillator is measured in
watt-sec
energy consumption in a home is measured in
kilowatt-hours
a closed loop must have
completed circuit with driving pressure (V), to force a current (I), to flow thru a resistance (R)
conductor
any substance that permits a flow of electrons (loosely attached and easily lost electrons)
current flow follows a gradient from
high voltage to low voltage
seeks path of least resistance
nonconductors or insulators
have tightly bound electrons which do not permit electron flow (glass, rubber, plastic, dry wood, pure water)
in direct current the electron flow is
always in the same direction
in alternating current the electron flow
reverses direction at regular intervals, measured in Hz (cycles per second)
when dealing with AC circuits the flow of current is opposed by
impedance
inductance generates
an electromagnetic field which creates increased resistance
capacitance generates
capacitance current in electrical circuit that creates a decrease resistance in the circuit
capacitance is
a measure of substance’s ability to store a charge
in DC circuit the capacitor plates are
charged by a voltage source and the flow of current is momentary
in AC circuit the capacitor plates
permits current of flow even when the circuit is not completed by a resistance
stray capacitance
power cord, consists of 2 insulated wires next to each other will generate capacitance just being plugged in
as frequency increases
impedance to electron flow will decrease
electrosurgical units use
high frequency currents so they have low impedance
a basic capacitor consists of
2 parallel conducting plates separated by an insulating layer (dielectric)
a capacitor is an electrical device used for
storing electric charge
what makes substances like iron, cobalt, and nickel magnetic
most of the electrons spin in the same direction
when electricity runs through a coil of wire
it produces a magnetic field
in an AC circuit, inductance can
electromagnetically generate an opposing electromotive force in a nearby wire
bending a wire into a coil
amplifies the magnetic field
the hot conductor
carries the current thru the impedance
the neutral conductor
returns the current to the source
the amount of current flowing thru the conductors depends on
the amount of impedance
high impedance
low current flow
low impedance
high current flow
a short circuit or fault is
a condition in which there is zero impedance with a high current flow
electric shock can occur
by contacting AC or DC current
electrical shock occurs when
a person becomes part of or completes an electric circuit
for a shock to occur
must contact the electric circuit at 2 points and a voltage source causing current to flow
in the OR there are 2 categories of electric shock
macroshock - large amount >1mA
microshock - small amount <1mA
a PA catheter with conducting fluid can
send current directly to the heart
how many mA can cause vfib
100-300mA in macroshock
100mmA in microshock
person contacts a 120V circuit with skin resistance of 1000 vs 100,000 ohms
120V/1000ohms = 0.12 amps = 120mAmps 120V/100,000ohms = .0012 = 1.2 mAmps
power is ___ in the OR
ungrounded
electrical equipment in the OR should be ___
always grounded
grounding of power and equipment provides
low resistance pathway for current during faults
