ARDMS Sonography Principles And Instrumentation (SPI) Practice Exam

To determine the dB value for an intensity that is reduced to three-quarters of its original value, it’s essential to understand how decibels (dB) are calculated in relation to intensity. The decibel scale is logarithmic and is used to express ratios of power or intensity. The formula to calculate the change in decibels (dB) when comparing two intensity levels is: dB = 10 * log10(P2/P1) where P2 is the new intensity, and P1 is the original intensity. In this case, if the intensity is reduced to three-quarters of its original value, we can express the ratio as: P2/P1 = 3/4 Substituting this into the formula gives: dB = 10 * log10(3/4) Calculating log10(3/4) yields approximately -0.1249. When you multiply by 10, you get about -1.249 dB. Therefore, rounding this to the nearest whole number gives -1 dB. This confirms that the reduction in intensity to three-quarters of its original value corresponds to a decrease of about -1 dB, which is why this choice is correct.