Radio Receivers - Engineering

Q1:

An unmodulated voltage 10 V effective is applied to a dioxide detector in which load resistance is 4 x 10-5 ohms. A micrometer shows that the rectified DC current in this resistance is 30 A. The efficiency of detection is

A 34%

B 55.5%

C 68.8%

D 84.7%

ANS:D - 84.7%

How is it? Please explain.