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Questions and Answers
What unit is used to measure electrical power?
Coulombs measure which of the following?
Which factor decreases electrical resistance in a circuit?
According to Coulomb's Law, what happens between like charges?
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What is primarily considered the biological resistor in electrical current flow?
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What does resistance indicate in a circuit?
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Which circuit type is characterized by having one path for current to flow?
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In a parallel circuit, what remains constant across all paths?
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What effect does increasing the surface area of an electrode have on current density?
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What is the primary purpose of inductance in a circuit?
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How does current density relate to the size of an electrode?
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Which of the following statements describes a characteristic of a series circuit?
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What typically influences the physiological effects of electrical stimulation?
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What is the primary role of the anode in a current flow system?
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What effect does increasing the output intensity have on the sensation of current at different points on the body?
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Which of the following correctly describes Ohm's Law?
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What happens to the strength of muscle contraction when the electrode is not firmly attached?
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Why is a moistened paper towel used with non-adhesive electrodes during experiments?
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What is the primary function of a conductor in an electrical circuit?
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In Part 2 of the experiment, how does the configuration of wet and dry electrodes impact the current sensation?
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What is the impact of resistance on current density in an electrical circuit?
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What type of current maintains a constant direction and positive or negative flow?
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What is the frequency range categorized as low carrier frequency?
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Which electrical modality uses a frequency range of 1001 - 10,000 Hz?
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What term describes the number of cycles of a waveform per second?
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In electrical modalities, what does a step-up transformer accomplish?
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Which waveform would be characterized by a unidirectional flow of ions?
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Which property of a waveform is defined by the height of the wave from the baseline?
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What best describes a finite period of charged particle movement in electrical currents?
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What characterizes a biphasic current in terms of ion flow?
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What does the interpulse interval refer to in pulsed current?
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What is the unit of measure for electrical current?
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Which statement accurately describes conductors?
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According to Ohm's Law, what does increasing resistance do to current flow?
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What constitutes a closed circuit?
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What is the term for the electrical potential difference between two poles?
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How is charge defined in the context of electrotherapy?
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If 120 volts of current produces a flow of 12 amperes, what is the resistance?
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Which of the following accurately states the relationship between electric charges?
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What is the role of the anode in an electrical circuit?
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What happens at the isoelectrical point?
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Study Notes
Foundations of Electrotherapy
- Electrotherapy is a safe and effective form of therapy when used appropriately.
- It’s an adjunct to other therapeutic modalities.
- Electrical stimulation is used with rehabilitation exercises.
Electrical Charges
- Charge is the electrical potential of an atom or ion.
- It is measured in Coulombs (C).
- Electrical Potential is the difference between charged particles at a higher and lower potential.
- Electrons are particles possessing a negative charge and small mass.
- Protons are particles possessing a positive charge.
Principles of Electrical Charges
- Two types of charges exist: positive and negative.
- Like charges repel, opposite charges attract (Coulomb's Law).
- Charge is neither created nor destroyed.
- Charges can be transferred from one object to another.
Conductors & Insulators
- Conductors are materials that transmit or allow the passage of electrical current: water, muscle.
- Insulators are materials that prevent or inhibit the passage of electrical current: skin, adipose.
- Conductance is the ease with which current flows along a conducting medium.
Electricity
- Electrical current takes the path of least resistance.
- Cathode is the negative pole with a high electron concentration.
- Anode is the positive pole with a low electron concentration.
- The imbalance in electrical charge allows the free movement of electrons between poles.
- Isoelectrical point is the baseline where electrical potential between two poles is equal and no electron movement occurs.
Closed Circuit
- A closed circuit is a complete uninterrupted path between two poles.
- Examples include flipping a light switch or electrical stimulating currents in the body.
Open Circuit
- An open circuit is an incomplete or interrupted path between two poles.
Electrical Current
- Electrical current is the net movement of electrons along a conducting medium.
- It is proportional to the magnitude of the force (voltage).
- Current always moves from higher potential to lower potential.
- Electrical current requires: a source of electrons, a conductor, and a driving force of electrons (voltage).
- Current Flow (I).
Ampere
- Ampere (A) is the unit of measure that indicates the rate at which electrical current is flowing.
- 1 Ampere (A) = 1 coulomb passing a point in 1 second.
- 20 coulombs passing in 1 second equals 20A.
Voltage
- Voltage is the electromotive force or potential difference between two poles.
- It measures the tendency for current flow to occur.
- Electrons move from one pole to the opposite, creating a potential for work which is calculated by Force x Distance.
- Volt is a measure of electrical power (V).
Ohms & Mhos
- Ohm is the unit of measure that indicates resistance to current flow.
- 1 ohm is the amount of resistance needed to develop 0.24 calories of heat when 1A of current is applied for 1 second.
- Mhos is the reciprocal of Ohms.
- Conductance is the ease with which current flows and is the mathematical reciprocal of resistance.
Ohm's Law
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Ohm's Law states: I = V/R
- Current flow = I
- Voltage = V
- Resistance = R
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Current flow is directly proportional to voltage and inversely proportional to resistance.
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Example: With a 120V current and a 12 A flow, the resistance is 10 ohms.
Electrical Power: Watt
- Watt is the measure of electrical power.
- It is the electrical power needed to produce a current flow of 1A at a pressure of 1V.
- Watt = Volts x Amperes.
Coulombs: Electrical Charge
- Electrical current results from the flow of electrons.
- Coulombs (Q) are a measure of the large number of electrons described as a single unit.
- They represent 6.28 x 10^18 electrons or protons.
- Coulomb's Law states the relationship between like and unlike charges: opposite charges attract and like charges repel.
Resistance
- Resistance (R) is the opposition to the flow of electrons by the material through which current travels.
- All materials have some degree of opposition to electrical flow.
- Skin is the primary biological resistor in electrical current flow.
- Resistance is measured in Ohms.
Factors Influencing Resistance
- Material of the Circuit: Conductors have less resistance.
- Length of the Circuit: Shorter distance equals less resistance.
- Cross-Sectional Area of the Circuit: Greater cross-sectional area equals less resistance.
- Temperature of the Circuit: Higher temperature equals less resistance (generally applies to wires, less evidence for tissue).
Impedance
- Impedance is the force that resists the flow of electrons and is related to resistance.
- It comprises three components:
- Resistance: Opposition to the flow of electrical current.
- Inductance: Ability of a material to store electrical energy by means of an electromagnetic field. It results from changes in charged particles.
- Capacitance: Ability of a material to store energy through the system. It arises from the storage of charge within the current.
Circuit Types
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Series Circuit:
- One path for current to flow from one pole to another.
- Often used for sensory-level stimulation.
- Electrode placement is close together, such as over a pain site or injury site.
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Parallel Circuit:
- Two or more routes for current to flow between poles.
- Often used for motor-level stimulation.
- Electrode placement is farther apart, such as over the origin and insertion of a muscle.
Series Circuits
- Electrons have one pathway to travel in a series circuit.
- Current remains the same in all components along the circuit.
- Resistance is equal to the sum of the individual resistors.
Parallel Circuits
- Electrons have alternate pathways to follow in a parallel circuit, choosing the path of least resistance.
- Electrons can branch into other parallel or series circuits.
- Each path has its own Amperage (A).
- Electrical flow in each path is inversely proportional to the resistance.
- Amperage varies but voltage remains constant.
Current Density
- Current density is the physiological effect of electrical stimulation related to the amount of current per unit area.
- Current density is inversely proportional to the size of the electrode.
- Greater surface area equals less current density.
- Less surface area equals greater current density.
Types of Electrical Currents
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Direct Current (DC):
- Galvanic flow of ions that flows in the same direction.
- Positive and negative.
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Alternating Current (AC):
- Current flow that periodically changes its polarity and direction of flow.
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Pulsed Current:
- Unidirectional or bidirectional flow of ions that ceases for a period of time before the next flow.
- Interpulse Interval: Period of time between pulses of ion movement.
Modality Generators
- Shapes Current Waveform: Creates the waveform, whether AC or DC.
- Creates Carrier Frequency: Determines the frequency of the electrical wave, as determined by the electrical modality machine.
Carrier Frequency
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Low: 0.1 - 1000 Hz
- Most electrical muscle stimulation.
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Medium: 1001 - 10,000 Hz
- Russian stimulation.
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High: 10,000 - ↑ Hz
- Diathermy.
Transformers
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Transformers change voltage in alternating current (AC).
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Step-up transformer: Allows an electrical device to operate from a lower voltage source.
- Hand-held modality units.
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Step-down transformer: Allows a device to operate from a higher voltage source.
- Wall modality units.
Waveform Terminology
- Amplitude: Intensity of the current. Height of the wave from the baseline. Measured in each individual waveform.
- Frequency: Number of cycles per second.
Phase & Pulse
- Phase: Portion of the wave that rises above or below the baseline.
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Pulse: Finite period of charged particle movement, separated from other pulses with periods of no current flow.
- Pulses can consist of one or more phases.
Alternating Current Impulses
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Biphasic Current:
- Bidirectional flow of ions.
- Includes a negative phase and a positive phase.
- Electrons move from negative to positive pole, reversing direction with polarity reversal.
- Cycle equals AC phase.
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Monophasic Current:
- Also known as Galvanic current.
- Uninterrupted unidirectional flow of ions toward a pole.
- Positive or negative.
Phase & Pulse Characteristics
- Phase Shape: Shape of the output current (Rectangular, Triangular, Spike).
- Phase Charge: Total electrical charge of a single phase (measured in coulombs).
- Pulse Charge: Amount of electrical charge of a single pulse (sum of the phase charges).
- Burst: Finite series of pulses flowing for a limited time, followed by no current flow.
Pulse Rate (Frequency)
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Waveform repeated at regular intervals.
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Number of events per second.
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For Direct Current: Frequency = Pulses per Second (pps).
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For Alternating Current: Frequency = Cycles per Second (cps) or Hertz (Hz).
Common Rates in Electrical Modalities
| Descriptor | PPS | Neuromuscular Effects |
|---|---|---|
| Low Motor | 1-10 pps | |
| High Motor | 20-50 pps |
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Description
This quiz covers the basics of electrotherapy and the principles of electrical charges. Understand the role of electrical stimulation in therapy and the properties of conductors and insulators. Test your knowledge on the fundamental concepts of electrical charges and their applications in rehabilitation.
