What is the standard unit for the phase charge in electrical stimulation?

• A. Coulomb
• B. Ampere
• C. Volt
• D. Ohm

Answer: (A)

Charge is the amount of electricity delivered in one stimulation phase. The standard SI unit for electric charge is the coulomb, defined as the amount of charge transferred by a current of one ampere in one second. In clinical practice for electrical stimulation, this is typically expressed in microcoulombs (µC) because the phase-delivered charges are small, with 1 µC equal to 10^-6 coulombs. The other quantities—ampere (current), volt (potential), and ohm (resistance)—describe different aspects of the system, not the total charge delivered. For example, delivering 1 mA for 1 ms gives Q = I × t = 0.001 A × 0.001 s = 1 × 10^-6 C, which is 1 µC. So the fundamental unit is the coulomb, with microcoulombs used for practical per-phase values.