Registered Physician In Vascular Interpretation (RPVI) Practice Exam

Transmit power reduced by factor 100; how many decibels?

-10 dB -20 dB -30 dB -40 dB

Correct Answer:

-20 dB

Explanation:

Decibels express ratios on a log scale, and for power the formula is dB = 10 log10(P2/P1). If power is reduced by a factor of 100, P2/P1 = 1/100. So dB = 10 log10(1/100) = 10 × (-2) = -20 dB. The negative sign simply indicates attenuation. In words: a 100× reduction in power corresponds to a 20 dB drop.

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