Thomas was a mariner, and working in defence force of his country. He was posted on the border of his country and has to look after the activity of the enemy in the sea. His work was made easier by the induction of SONAR in his ship. What should be the frequency of the transmitter of SONAR needed to do the job?
(a.) 10,000 Hz
(b.) 20,000 Hz
(c.) 40,000 Hz
(d.) 50,000 Hz
