A stretched string of length L is observed to vibrate in four equal segments when driven by a 688-Hz oscillator. What oscillator frequency will set up a standing wave so that the string vibrates in two segments

sonar - device which is used to find the submit submarines, sankalp ship. sonar waves consists of a transmitter and detector which are installed in the observation centre on board of a ship. the ultrasonic waves are sent into the sea at high frequency about 1000 khz in all direction.

i think the answer is a and b

i wish you luck

option number c is the right answer.