The sound of heart beats (or lungs) reaches the doctors ears by the _________________ of sound waves through the stethoscope tube.

SONAR stands for ______________.

If there are some cracks and flaws in the metal blocks, which are _________________ from outside reduces the strength of the structure can be detected by using ultrasound.

Low pressure regions of sound waves are known as  ________________________.

The disadvantages of reverberation are ______________ .

Ultrasound is used to investigate the internal organs like ______________of human body.

Which of the following are correct :

(a) Ultrasounds are low frequency waves.

(b) Ultrasounds are high frequency waves.

Which of the following are correct :

(a) Sound Board is a concave board (curved board) placed behind the stage in big halls.

(b) Sound Board is a convex board (curved board) placed behind the stage in big halls.

Which of the following are correct :

(a) Megaphone is large cone shaped device used to amplify and direct the voice of a person who speaks into it.

(b) A horn is a cone shaped instrument used for signalling in bicycles, cars, buses, etc.

Which of the following are correct :

(a) Echoes may be heard more than once due to successive multiple reflections.

(b) To hear an echo, our distance from the reflecting surface should be atleast 17.2 m.

(c) To hear an echo, our distance from the reflecting surface should be atleast 34.4 m.