5. It is a matter of common experience that when we utter a few words in a high domed hall, the words are repeatedly heard on account of reflection from the walls of the dome. This is what we call an echo. An echo is the phenomenon of repetition of sound of a source by reflection from an obstacle. An echo can be distinguished from the original sound, if the obstacle is situated at a suitable distance from the source of sound.

7. As total distance travelled by sound = speed of sound x total time 2 d = v x t Substituting v = 344 m/s (speed of sound in air at 20 degrees Celsius) t = 1/10 s, we get 2 d = 344 m/s x 1/10 s = 34.4 m Therefore, d = 17.2 Hence, for hearing a distinct echo, the minimum distance of the obstacle from the source of a sound should be 17.2 m*. * The distance changes with the change of temperature of air!

8. We have all been in cinemas, theatres etc., can we think of what would happen if sound reflection was not taken care of properly? Would we be able to watch a movie or play as effectively as we are able to do? So, we know come to think about how exactly do they control this reflective effect? Firstly, the ceilings of these halls are curved. This enables the sound to reach all corners of the hall after reflection from the ceiling.

18. What are the disadvantages of sonar? What is a FATHOMETER? Please explain. Does ECHOCARDIOGRAPHY have any harmful effects on our body? How does ultrasound cure neuralgic pains? What cavitation and cold boiling? What is the purpose of detecting flaws and cracks in metal blocks? How does HPU treat hypothermia? What is cell disruption in HPU?