A stone is dropped from the top of a tower $500$ m high into a pond of water at the base of the tower. When is the splash heard at the top? Given, $g = 10$ m s$^{-2}$ and speed of sound = $340$ m s$^{-1}$.
3.
Explain how defects in a metal block can be detected using ultrasound.
4.
What is sound and how is it produced?
5.
Describe with the help of a diagram, how compressions and rarefactions are produced in air near a source of sound.
6.
Does sound follow the same laws of reflection as light does? Explain.
7.
What is loudness of sound? What factors does it depend on?
8.
When a sound is reflected from a distant object, an echo is produced. Let the distance between the reflecting surface and the source of sound production remains the same. Do you hear echo sound on a hotter day?
9.
What is reverberation? How can it be reduced?
10.
A sound wave travels at a speed of $339$ m s$^{-1}$. If its wavelength is $1.5$ cm, what is the frequency of the wave? Will it be audible?
11.
The frequency of a source of sound is $100$ Hz. How many times does it vibrate in a minute?
12.
Flash and thunder are produced simultaneously. But thunder is heard a few seconds after the flash is seen, why?
13.
Give two practical applications of reflection of sound waves.
14.
Which characteristic of the sound helps you to identify your friend by his voice while sitting with others in a dark room?
15.
How is ultrasound used for cleaning?
16.
A person has a hearing range from $20$ Hz to $20$ kHz. What are the typical wavelengths of sound waves in air corresponding to these two frequencies? Take the speed of sound in air as $344$ m s$^{-1}$.
17.
Two children are at opposite ends of an aluminium rod. One strikes the end of the rod with a stone. Find the ratio of times taken by the sound wave in air and in aluminium to reach the second child.
