An ultrasound system is set to 0db and is transmitting at full intensity. What is the output power when the system is transmitting at 10% of full intensity?

• A. -3 dB
• B. -50 dB
• C. 40 dB
• D. -10 dB

Answer: (D)

The concept being tested is how percent power relates to decibels. If the system is at full intensity, that’s our reference (0 dB). Dropping to 10% of that power means the power ratio is 0.1. In decibels, this ratio is 10 log10(0.1) = -10 dB. So the output power is -10 dB relative to full intensity. The other options don’t fit because -3 dB corresponds to about 50% power, -50 dB is an extremely small fraction (~0.001%), and +40 dB would imply a power thousands of times greater than the full reference, not a reduction.