Question -
Q. Consider the following statements with reference to sound:
Sonic boom is caused by an object travelling at supersonic speed.
Unlike light, sound does not reflect from a harder flat surface called specular reflection.
Principle of reverberation of sound is used in the stethoscope to hear a patient's heartbeat.
Which of the above given statements is correct?
Options:
A .  1 and 2 only
B .  2 only
C .  2 and 3 only
D .  1 and 3 only
Answer: Option D : D Explanation: Statement 1 is correct: When an object travels at a speed greater than the speed of sound in air, it is said to be travelling with a supersonic speed. Enormous energy is produced when an object travels at a supersonic speed. This energy is propagated as a sharp and loud sound, called a sonic boom. Statement 2 is incorrect: When the sound wave is reflected by a surface then the incident wave, reflected wave and the normal at the point of incidence all lie in the same plane. Similar to reflection of light from a mirror, sound also reflects from a harder flat surface. This is called specular reflection. Both light and sound reflects from a harder flat surface. Statement 3 is correct: Reverberation is the phenomenon of persistence of sound (though the source has stopped producing sound) as a result of multiple reflections from a closed surface. Stethoscope which is used to hear the sounds of internal organs of a patient works on the principle of reverberation.
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