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Answer :

Loud sounds have high energy. Loudness directly depends on the amplitude of vibrations. It is proportional to the square of the amplitude of vibrations of sound.

- What is sound and how is it produced?
- Describe with the help of a diagram, how compressions and rarefactions are produced in the air near a source of sound.
- Cite an experiment to show that sound needs a material medium for its propagation.
- Why sound wave is called a longitudinal wave?
- Which characteristics of the sound help you to identify your friend by his voice while sitting with others in a dark room?
- Flash and thunder are produced simultaneously. But thunder is heard a few seconds after the flash is seen, why?
- 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.
- 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 the air and in aluminium to reach the second child.
- The frequency of a source of sound is 100 Hz. How many times does it vibrate in a minute?
- Does sound follow the same laws of reflection as light does? Explain.
- 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?
- Give two practical applications of reflection of sound waves.
- 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.
- A sound wave travels at a speed of 339 m/s. If its wavelength is 1.5 cm, what is the frequency of the wave? Will it be audible?
- What is reverberation? How can it be reduced?
- Explain how bats use ultrasound to catch prey.
- How is ultrasound used for cleaning?
- Explain the working and application of a sonar.
- A sonar device on a submarine sends out a signal and receives an echo 5 s later. Calculate the speed of sound in water if the distance of the object from the submarine is 3625 m.
- Explain how defects in a metal block can be detected using ultrasound.
- Explain how the human ear works.

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