Sound Waves And you Sound waves Longitudinal waves

Sound Waves And you

Sound waves • Longitudinal waves = particle motion in same direction as energy motion • Hearing ~ 20 to 20, 000 Hz (sound generator) • http: //plasticity. szynalski. com/tone-generator. htm • Loudness = amplitude • Pitch = frequency • Rubens tube: tone generator

Follow up question • A) A Rubens tube filled with propane gas has a measured λ of 1. 81 m when a tone of 246 Hz is used. What is the speed of the sound wave in the propane?

The answers • A) 445 m/s

Closed tube waves • 1 st mode = ¼ λ node at closed end anti node at open end 1 st harmonic (overtone) antinode L=¼λ 2 nd harmonic 3 rd harmonic L=¾λ L = 5/4 λ

How can we write a general equation • That takes into consideration: ¼, ¾, 5/4 … • That is similar to the equation we used for waves on a rope? • L = n/2 wavelengths

Odd series of #s math relationship • 2 n – 1 • L = (2 n – 1) /4 λ • λ = v/f • So the L = (2 n – 1) / 4 v/f

A quick question then… • If a 6 th mode wave is generated in a closed end tube with a length of 7 m, then what is the wavelength of the wave generated in the tube? • ~ 2. 55 m

In the lab you work on – you will need to include a correction factor in your calculations. • You will measure the length of the closed end tube = measured L • You will incorporate a correction factor to calculate the “corrected L” • The corrected L = measured L + (diameter of the tube x. 4)

• B) The first fundamental frequency is produced in a tube with a measured length of 0. 32 m and a diameter of 11 cm using a 247 Hz tone. • A) What is the wavelength of the wave generated in the tube? (do not forget the correction factor!!!) • B) What is velocity of the wave in the tube? • A) 1. 456 m = wavelength • B) 359. 6 m/s = velocity

What is the velocity of sound in the air around us? ? • Well that value is temperature dependent. . • The relationship that can be used to determine the velocity of sound in the air around us is: • V = 331 m/s + (. 6 m/s x every 1 O above OO C)

More fun questions • A) If the temperature of a room filled with air is 32 OC (at one atmosphere of pressure), what is the velocity of a sound wave in the room? • The answer: 350. 2 m/s • 331 m/s + (. 6 x every 1 O above OO C)

So you can see there are 2 possible ways to calculate the velocity of the wave in the air • You will be asked to do both on the lab.

Acoustics • https: //www. youtube. com/watch? v=JPYt 10 zrcl. Q