Why is there a difference between the sound produced by blowing into the mouth of a small homoeopathic vial or key and the mouth of an empty test tube?
Answer: Blowing into the mouth of a small homoeopathic vial or key produces a shrill sound, but blowing into the mouth of an empty test tube produces a coarse or deep sound. The shorter the length of the vibrating air column in smaller keys, the higher the frequency of the sound produced. Hence the sharp sound is heard.
But because the length of the vibrating air column in the test tube is longer, the frequency of the sound produced is lower. Because of this, a relatively thick or serious sound is heard.