Zap Through the Electrotherapy 2026 US Practice Test – Electrify Your Knowledge!

ERA is the portion of the transducer surface that actually emits ultrasound energy. It is set by the crystal’s size—the diameter of the crystal determines the effective radiating area. This radiating surface is used to calculate intensity (I = power divided by ERA), so a larger crystal increases ERA and changes the delivered intensity for the same power. The outer boundary of the transducer isn’t the radiating area, the depth of tissue penetration is determined by frequency and tissue properties rather than ERA, and the maximum power setting affects total energy, not the actual radiating surface.