Ohm's Law and Circuit Principles

Ohm's Law

• Ohm's Law describes the relationship between current, voltage, and resistance.
• I = V/R (Current equals Voltage divided by Resistance)
• Current (I) is directly proportional to voltage (V)
• Current (I) is inversely proportional to resistance (R)
• Current (I): the rate of flow of electrically charged particles (electrons in metals, ions in biological tissues). Measured in Amps, milliamps, or microamps.
• Voltage (V): the driving force that causes charged particles to move. Measured in volts or millivolts.
• Resistance (R): the opposition to current flow. Measured in Ohms.

Constant Current vs. Constant Voltage

• Constant Current: Devices maintain a consistent current output, regardless of changes in resistance.

  • Advantage: Provides a consistent physiological response, similar to cruise control.
  • Disadvantage: If electrode contact is lost or compromised, current concentrates in the areas with contact.

• Constant Voltage: Devices maintain a constant voltage output. Current changes as resistance changes.

  • Disadvantage: The quality of the response varies with changes in resistance, potentially making the treatment less effective or comfortable.

Waveforms

• Description: Waveforms are graphic representations of electrical current characteristics, including amplitude, duration, and frequency.
• Interpretation: Waveforms visually illustrate the specific characteristics of the electrical current.
• Monophasic: Current flows in one direction (either anode to cathode or cathode to anode) the entire time. Produces a polarity effect.
• Biphasic: Current changes direction. Produces a polarity effect only if unbalanced.
• Polarity: Electron flow in one direction (monophasic, and sometimes with unbalanced biphasic waveforms). One electrode is positive, the other negative.
  • Therapeutic Applications (greatest to least effect): Iontophoresis (DC), acute edema (HVPC), NMES (pulsed current: biphasic asymmetrical unbalanced waveform).
  • Advantage of Polarity: Can make one electrode more active than another.
  • Disadvantage of Polarity: Potential for discomfort or burns.
• Direct Current (DC): Constant flow of electrons in one direction for more than a second. Polarity is based on the intended treatment outcome.
• Alternating Current (AC): Continuous flow with current constantly reversing from positive to negative. Sinusoidal pattern.
• Pulsatile: Non-continuous flow with pulses in one direction (monophasic) or both directions (biphasic). Biphasic can be balanced (no polarity) or unbalanced (mild polarity effect).

This quiz covers the fundamentals of Ohm's Law, including the relationships between current, voltage, and resistance. It explores constant current versus constant voltage principles, providing an understanding of how these concepts apply in electrical circuits. Perfect for students looking to test their knowledge in electrical engineering concepts.