How sound is transmitted (in gas / solid)
As an experiment of changing the sound transmitted through the gas, the experiment of changing the voice using helium gas is famous. I think the students have heard a high voice once. Using this, we will experiment with the mass of gas and how sound is transmitted using carbon dioxide.
Experiment 1: Pitch of sound transmitted through gas
you need : 2 tubes (or test tubes), carbon dioxide
Prepare two tubes of the same length and thickness as shown in the photo above. Put carbon dioxide in one. The other is air. ① Remind students of their voice when they inhale helium gas. (Being high and helium is light) (2) Blow the air cylinder several times as shown in the picture to memorize the sound. ③ Check the difference in weight of air, carbon dioxide, and helium. ④ Blow after predicting the sound in the case of carbon dioxide. (The sound will be low.)
The speed of sound of gas
The sound transmitted through the gas is as shown in the formula on the left. ρ is the density. P is a constant (constant due to atmospheric pressure). In general, the denser the gas, the slower the speed, and the lower the density, the faster the speed. As helium, air, and carbon dioxide become heavier, the speed slows down and the sound changes.
The frequency of gas has a relationship of V (sound velocity) = f (wavelength) x λ (frequency).
Solving the frequency gives λ = V ÷ f. Since the length of the trachea that makes a human voice is fixed, the value of f does not change. The higher the speed of sound V, the higher (higher) the frequency λ.
Experiment 2: Listen to bone conduction sounds!
If you listen to your own voice with tape etc., it sounds strange. This is because my voice is usually heard as a mixture of the sound emitted from the vocal cords transmitted through the air (in gas) and into the ears, and the sound transmitted through the skull (in solid). This is because the voice of the tape can be heard only through the air. Experiment with sounds transmitted through bones such as the skull.
Sound like bone conduction sound
you need : spatula, octopus thread, paper cup
This is a way to let the class hear a sound close to bone conduction sound. Put octopus thread on the spoon and hit it. I can only hear a dull sound. When you hit it with a paper cup, it looks like a bell. This is because the sound transmitted from the octopus thread (solid) was emitted from the paper cup into the air. It is not bone conduction, but it is a sound that is partially transmitted through solids.
Bone conduction sound
Make a loop on the octopus thread attached to the spoon. Put your index finger in the ring and put your index finger in your ear. And hit. You can hear a clean and clear sound. Bone conduction sound.
There are some students who do not understand the part that is transmitted through the bones because they are heard from the ears. There, I hear a full-fledged bone conduction sound.
Connect the motor to a sound source such as a radio cassette player. Make a hole in disposable chopsticks and insert it into the rotating shaft of the motor. When you hold it in your mouth, you can hear the sound firmly. Since it does not pass through the ear, I am convinced that this is bone conduction.
Experiment 3: Let's make various tin can phones
you need : Many paper cups, wires, springs, balloons, crystal earphones 2
① Wire phone: This can be heard even if the wire is bent as well as the sound quality. You can also hear your own voice. ② Spring call: When you extend the spring and release your hand during a call, you can hear the invader sound effect. ③ Balloon phone: Sounds better than a tin can phone. The air conveys the sound. (4) Crystal earphone telephone: A piezoelectric element transmits sound as an electric signal. It's a strange tin can phone.