electricity Flashcards
what is electricity
the effects produced by moving charges
SI unit of charge is the
coulomb (C)
positively charged contains ___ protons than electrons
more
negatively charged contains ___ protons than electrons
less
fundamental principle of charge interaction
positively charged object will attract a negatively charged object
Coulomb’s law
the magnitude of the electrostatic force of attraction or repulsion
a current going down a line is __ energy
kinetic
electrical current is defined as
the amount of charge flowing per unit time
materials in which charges can easily move
conductor
an amp of current corresponds to
1 coulomb of charge per second
to be a good conductor,
electrons must be able to move easily from one atom to the next
most insulators are ___ and generally not good conductors except for
graphite
the energy required to push electrons though a material is a measure of the
resistance
resistance is measured in
ohms
ohm’s law relates
electrical potential = impedance x resistance
the reciprocal of resistance is
conductance
conductance is measured in
mhos
electric circuit
the closed path through which a charge flows
direct current (DC) circuit
an electrical circuit in which the current flows in one direction only
alternating current (AC) circuit
an electrical circuit in which the current reverse its direction in a periodic fashion
short circuit
A situation in a circuit where the normal resistance of the circuit is bypassed by a low resistance path resulting in a large current
series circuits - when batteries or resistors are connected in a series, the voltages and resistances are
added
when resistors are connected in parallel,
current flows through each resistor independently of the other
power =
the rate of using energy. energy/time.
diodes
Diodes are circuit elements that have large conductance’s in one direction and a smaller in reverse. Used to control the current direction. Effective diodes can be made having p-type nad n-type regions next to each other.
forward bias (?)
n region negative, p region positive… slide 31
reverse bias (?)
has depletion region and high resistance
transistor
used to amplify or switch currents
macroshock
large amt of current conducted thru a patients skin or other tissues. the extent of injury will depend on the amt of current and the duration of the exposure
microshock
the delivery of small amt of current directly to the heart.
microshock is a risk for
v-fib (<50 uA)
v-fib can be produced by a current that is below the threshold of human perception
1 mA
polarized plug
one narrow(high potential) one wide prong (low potential) so they can only go in the wall the correct way.
three-pronged grounded plug
some electrical devices have a rounded third prong that is connected to ground when plugged into a three-pronged receptacle. This third prong is wired directly to the casing of the electrical device. if for some reason a high-potential wire comes into contact with the case, the current will flow directly though the third prong instead of through your body.
ground fault circuit interrupter
used in circuits near water sources. GFCIs immediately (within 1ms) disrupt the flow of current in the circuit if a change in current is detected.
disadvantage of GFCI
interrupts the power without warning - the defective piece of equipment can no longer be used, which might be a problem if it were necessary for life support
ground systems - risk to humans
humans who are at ground potential because of what they are touching have to only touch a single object to complete a circuit, resulting in shock.
to further decrease the risk of of electrical shock, electrical systems are ___ from the grounded electrical supply through the use of isolation transformers
isolated
isolation transformers
rely on magnetic inductance to transfer a current from the grounded electrical system to an ungrounded secondary system without the two systems physically contacting each other.
line isolation monitor
Alarms when a fault in an ungrounded system occurs- piece of equipment is causing a ground. a second fault can result in a shock
line insolation monitors are located
between live wires and a ground so that the impedance to current flow can be measured.
alarm set point for line isolation monitor is between
2-5
which two factors determine installing an isolated power
is the operating room a wet location? and if so is an interruptible power supply acceptable?
___ is used to convert grounded power to ungrounded power
isolation transformer
_____ warns that isolation of the power from ground has been lost in the event that a defective piece of equipment has been plugged into one of the isolated circuit outlets
line isolation monitor
