Reflection of Sound
Sound waves also follow the laws of reflection just like the light waves.
According to the law of reflection, the angle of incidence of the sound wave with the normal is equal to the angle of reflection with the normal. In case if a wave is incident perpendicular to the surface then the reflected sound will travel back in the opposite direction along the same line.
Law of Reflection
We can even perform an experiment to verify that sound waves follow the laws of reflection.
Experiment: Reflection of Sound
Take two small hollow cylindrical shaped objects which are open from both ends. Place them on the table near the wall as shown in the figure below. We also need to make sure that the table is covered with white cardboard paper before keeping the pipes on it. Place a running clock near the open end of the pipe facing you. And now keep your ear near the open end of the other pipe.
Experiment: Reflection of Sound
You will hear the sound of the ticks coming from the pipe. Adjust the pipes until the sound is clearer. A point will come when you can clearly hear the sound of the clock ticking.
The sound that you hear is the reflected sound. The sound wave from the clock passes through the pipe and is incident on the wall. It gets reflected and passes through the other pipe and enters your ear. You will notice that these two angles are approximately equal. That is, the angle of incidence will be equal to the angle of reflection if we ignore any human errors.
Echo
The repetition of sound caused by the reflection of the sound waves is called an echo. We usually hear it in empty spaces bounded by at least one tall surface. For example when we are inside a large canyon, or when we are shouting in a deep empty well from above.
If we clap in an open space standing against a tall wall, we will also hear the sound of our clap again and again. This is because the sound from our clap travels in all the possible directions and when it collides with the obstacle, it gets reflected back. These reflected sound waves then travel towards us and we hear faint repetitions of our clap again and again.
There are certain conditions that are necessary in order to hear an echo. We will learn about those conditions in the upcoming segment.