If power increases, what happens to amplitude and intensity?

• A. They decrease
• B. They both increase
• C. They remain unchanged
• D. Only amplitude increases

Answer: (B)

Power is the rate at which energy is delivered, and intensity is that power per unit area (I = P/A). The amplitude of the wave—often described by the peak pressure or particle velocity in ultrasound—is linked to how much energy the wave carries, with intensity proportional to the square of the amplitude (I ∝ A^2). So when power increases, the energy carried by the beam goes up, and if the beam area remains the same, the intensity rises. Since intensity grows with the square of the amplitude, the amplitude must also rise (amplitude ∝ sqrt(I) ∝ sqrt(P)). Therefore, both amplitude and intensity increase as power increases.