Basic Principles of Electricity (Part 1) Flashcards
What is an electric current?
A flow of charged particles. Electrons in metal and ions in the human body
What is capable of propelling the charged particles in an electric current from higher to lower energy levels?
Electrical force
Increased ions produces _____ potential electrical energy
increased
What does Q stand for?
electrical charge
What is charge measured in?
coulombs
3 fundamental concepts about electric charge
1) Like charges repel, opposite charges attract
2) Charge can be transferred
3) Charge cannot be created, nor destroyed
What are ions?
elements with either an excess or a deficiency of electrons
__ions are positively charged ions (Na+, K+) and __ions are negatively charges ions (Cl-)
cations
anions
What does polarity indicate?
relative charge
An ____ is a positively charged electrode whereas a ____ is a negatively charged electrode
anode
cathode
Anodes attract ____ ions whereas cathodes attract _____ ions
negative
positive
What does I stand for?
Current
Define current
The rate of flow of charged particles
What is current measured in?
amperes
What does current (I) equal?
Current (I) = Charge (Q) / Time (t)
Current travels from the __ode to the __ode
anode –> cathode
Define voltage
the force resulting from an accumulation of electrons at one point in an electrical circuit.
aka the intensity or strength of the current
What does Ohm’s Law state?
the current in an electrical circuit is directly proportional to the voltage and inversely proportional to the resistance
Current flow (I) = Voltage (V) / Resistance (R)
What do watts indicate?
The rate at which electrical power is being used
Resistance increases as the cross sectional area ____ and its length _____
decreases
increases
Materials that permit free movement are called what?
conductors
Materials that resist current flow are called what?
insulators
define conductance
the ease with which current flows along a conducing medium
Of the following which are good and which are poor at conducting?
Skin Fat Blood Muscle Bone Nerve
- Skin is poor
- Fat is poor
- Blood is the best
- Muscle is good
- Bone is the poorest
- Nerves are good
Tissues high in what are considered good biologic conductors?
water
What is capacitance?
The property that allows the system to store charge
What is impedance?
The opposition to alternating currents
Higher frequency of stimulation = _____ impedance of tissues
lower
What is an electrical circuit?
The path of current from a generating power source through various components back to the generating source
In a ____ circuit electrons are flowing, and in an ____ circuit the current flow ceases.
closed
open
What are the 2 patterns in which components that provide resistance to current flow may be connected to one another?
- series
- parallel
What is the difference between an series and parallel circuit?
In a series circuit there is only one path for current to get from one terminal to another. In a parallel circuit, two or more routes exist for current to pass between the 2 terminals
How are the component resistors arranged in a series circuit?
end to end
In a series circuit the total resistance to current flow is equal to what?
The resistance of all of the components added together
What happens to the voltage as it passes through each component of a series circuit?
It decreases such that the sum of the voltage decreases is equal to the total voltage
How are the components arranged in a parallel circuit?
side by side and the ends are connected
Each component resistor is a parallel circuit receives the ___ voltage
same
What does the current passing through each component of a parallel circuit depend on?
its resistance
With each component added to a parallel circuit the total resistance _____.
decreases
Component resistors connected in series have a ____ resistance and a ____ current flow
higher
lower
Component resistors connected in parallel have a ____ resistance and a ____ current flow
lower
higher
Is the electrical current that exists when electrons flow through human tissue a series or parallel circuit?
A combination or the 2
What are the 3 types of current?
- direct
- alternating
- pulsed
What is a direct current?
an uninterrupted unidirectional flow of electrons toward the positive pole
A direct current must last for at least how long?
1 second
What can a direct current be used for clinically?
- Iontophoresis
- Wound healing
- Stimulation of denervated muscle
What is an alternating current?
the continuous or uninterrupted bidirectional flow of electrons
Electrons flowing in an AC always move from _____ to _____ pole
negative to positive
An alternating current must last for at least one second and also do what?
cross the isoelectric line at least twice in 1 second
What can an alternating current be used for clinically?
Stimulation of denervated muscle
What is a pulsed current?
the grouping of three or more pulses either unidirectionally or bidirectionally that are interrupted for short periods of time and repeat themselves at regular intervals
What can a pulsed current be used for clinically?
- IFC
- Russian currents
*not for iontophoresis
Describe monophasic waveform
current flow is on one side of the isoelectric line
Describe biphasic waveform
current flow is first on one side of the isoelectric line and then changes to the opposite side
What is a pulse?
an individual waveform
What is a phase?
The portion of the pulse that rises in one direction either above or below the baseline for some period of time
Because a direct current only have a single pulse duration and phase duration it is referred to as a ____ current
monophasic
With direct current the terms single pulse duration and phase duration indicate what?
the length of time that current is flowing
Because an alternating current produces waveforms that have two separate phases during each individual cycle it is referred to as a ____ current
biphasic
Are pulsatile currents monophasic or biphasic?
They can be either
In a PC single pulses are interrupted by what?
interphase intervals
In a PC what does the pulse duration equal?
The sum of all phases plus the interphase interval
In a PC the time during which the current is not flowing between the two phases is called what?
Interpulse interval
What does a pulse’s amplitude refer to?
The intensity of the current with reference to the isoelectric line, with the maximum amplitude being the highest point of each phase
Amplitude is synonymous with what 2 other terms?
“current intensity” and “voltage”
How can average current be low with high peak amplitudes in a PC?
Due to long interpulse intervals
What is pulse charge?
the total amount of electricity being delivered to the patient during each pulse
The phase charge and the pulse charge are the same and always greater than zero in a ___phasic current
monophasic
The pulse charge is equal to the sum of the phase charges in a ___phasic current
biphasic
What is the net pulse charge on a symmetrical biphasic current?
zero
What does phase duration indicate?
The elapsed time between the beginning and end of one phase
What is pulse duration?
The elapsed time between the beginning and ending of all phases in a single pulse (aka pulse width)
With ___phasic current, the phase duration is the same as the pulse duration.
monophasic
With ___phasic current, the pulse duration is determined by the combined phase durations.
biphasic
What does rise time refer to?
how quickly the pulse reaches its max amplitude in each phase
What does decay time refer to?
the time in which a pulse goes from peak to zero volts
The combined time of the pulse duration and the interpulse interval is referred to as what?
In other words what is the elapsed time from a given point on one pulse to the same point on the succeeding pulse referred to?
Pulse period
What does pulse frequency indicate?
The number of pulses per unit of time
What is a burst
a finite series of pulses over a finite interval of alternating current at a specific frequency over a specific period of time
What does current modulation refer to?
Any alteration in the amplitude, duration, or frequency of the current during a series of pulses or cycles
What are the 4 types of current modulation?
- Continuous
- Burst
- Beat
- Ramping
Describe continuous current
The amplitude of current flow remains the same over time and is usually associated with long-pulse-duration monophasic current
Describe burst modulation
Occurs when a PC or AC flows for a shirt duration and then is turned off for a short time
What are the interruptions between individual burst called?
Interburst intervals
Describe beat modulation
Prodcued when two interfering biphasic current waveforms with differing frequencies are delivered to two separate pairs of electrodes through separate channels within the same generator
How are the 2 pairs of electrodes arranged for beat modulation?
In a crisscrossed or cloverleaf-like pattern so the circuits interfere with one another
Beat-modulated alternating current is referred to as what?
IFC or premodulated interferential
Describe ramping modulation
The current amplitude will ramp up gradually to some preset maximum and may also ramp down in intensity
What is the ramp-up time usually preset at?
About 1/3 of the on time
Are motor nerves stimulated by a steady flow of direct current? Why or why not?
No, because the nerve repolarizes under the influence of the current and will not depolarize again until a sudden change in current intensity occurs
What does frequency indicate?
The number of impulses (cycles) produced by an electrical stimulating device in 1 second and is referred to as cycles per minute (CPS)
What two muscle characteristics are a function of the frequency?
The amount of shortening of the muscle fiber and the amount of recovery allowed to the fiber
Increasing the intensity of the electrical stimulus causes what?
The current to reach deeper into the tissue
Are high- or low-volt currents more capable of penetrating deeper into the tissue?
high-volt
How can you stimulate more nerve fibers with the same intensity?
Adjust the duration of the treatment
The negative electrode that has a high number of electrons is called what?
the cathode
The positive electrode that has a low number of electrons is called what?
the anode
