Which term is described as the unit used to compare the ratio of intensities or amplitudes of two sound waves?

• A. Amplitude
• B. Density
• C. Duty factor
• D. Energy

Answer: (A)

Decibels express the ratio between two sound waves, turning a comparison into a manageable, logarithmic scale. The relationship differs slightly for amplitude and for intensity: a change in amplitude uses 20 log10(A1/A2), while a change in intensity uses 10 log10(I1/I2). This is why small changes in amplitude or power can correspond to noticeable changes in decibels. For example, doubling the amplitude is about +6 dB, and increasing intensity by a factor of ten is +10 dB. In ultrasound practice, decibels are used to describe gains, attenuation, and dynamic range, making it easier to compare strengths across different conditions. The term listed for a unit of ratio is not amplitude, which describes the size of a single wave, nor are density, duty factor, or energy appropriate as a unit for comparing wave ratios.