Chapter 16: Sound

Course Overview http://chem.winthrop.edu/courses Webpage Syllabus Class notes The Class time is 75 minutes MWF No Cell phones, tablets or Computers are allowed in class Office: SIMS, 203 Office Hours: T 10:00-11:00, W 1:00 - 3:00, or by appointment

Webpage and Class notes http://chem.winthrop.edu/

Syllabus- Attendance Although roll is not formally taken in class, I strongly recommend regular attendance. The course has a significant component of interactive learning, and the activities done in class reinforce the material discussed. If there is a reason that you must miss class please talk with me to make arrangements to cover the material. The attendance policy described in the Winthrop University undergraduate catalog will be followed.

Homework Homework problems are due on the dates indicated on the class calendar. Your work is due on time, with the exception of reasonable documented excuses. Late work will be docked 50% of face value and 100% after solutions have been posted. if I notice that the homework is copied from the solutions manual, I will not grade it, and the 5% homework grade will be added to the exams grade.

Quizzes-Recitation Lecture: The PHY 212 lecture is a flipped model class, you are required to read the chapter’s parts in the schedule posted online before coming to class, I will show videos, explain the concepts and solve problems. There will be a 20 minutes quiz every Friday at the beginning of lecture. The equations are not provided for the quizzes. There will be a recitation on Tuesdays at 11:00am in SIMS 207

Exams There will be three in class exams and a final. The three exams are 75 minutes duration. Notes and your book are not allowed during the exam. All relevant equations and physical constants will be provided. The final exam will be two hours and 30 minutes and will cover early portions of the course so you must review the entire course material.

Grading: Homework 5% Three in Class exams 10% each Quizzes 10% If you are going to miss a test, you must notify me in advance (preferably one week) so alternate arrangements can be made. If you miss a test and your absence is not excused, a grade of zero points must be assessed for that particular piece of work. You must take the 75 minutes exams as well as the final exam in order to pass the course. Grading: Homework 5% Three in Class exams 10% each Quizzes 10% Final Exam 30 % Lab 25%

Labs Labs start on Tuesday, January 16, 2018 Do not miss any laboratory. You will receive "0" for all missed laboratories. Lab exam is on the last day of classes. Lab exam is 25% of the total lab grade

16-1 Characteristics of Sound: Sound https://www.youtube.com/watch?v=GkNJvZINSEY

16-1 Characteristics of Sound Sound is a longitudinal wave Loudness: related to intensity of the sound wave (energy transported by the wave per unit time across unit area) Pitch: related to frequency Audible range: about 20 Hz to 20,000 Hz; upper limit decreases with age Ultrasound: above 20,000 Hz   at room temperature

16-1 Characteristics of Sound: Problem 3 3.(I) (a) Calculate the wavelengths in air at 20°C for sounds in the maximum range of human hearing, 20 Hz to 20,000 Hz. (b) What is the wavelength of a 15-MHz ultrasonic wave?

16-3 Intensity of Sound: Decibels The intensity of a wave is the energy transported per unit time across a unit area. The human ear can detect sounds with an intensity as low as 10-12 W/m2 and as high as 1 W/m2,(Watts/m2) Perceived loudness, however, is not proportional to the intensity.

16-3 Intensity of Sound: Decibels The loudness of a sound is much more closely related to the logarithm of the intensity. Sound level is measured in decibels (dB) and is defined as: Where I0 is taken to be the threshold of hearing (Watts/m2): The unit of the sound level β is decibel (dB)

Problem 8 8. (II) A person, with his ear to the ground, sees a huge stone strike the concrete pavement. A moment later two sounds are heard from the impact: one travels in the air and the other in the concrete, and they are 0.75 s apart. How far away did the impact occur? See Table 16–1.

16-3 Intensity of Sound: Decibels Example 16-3: Sound intensity on the street. At a busy street corner, the sound level is 75 dB. What is the intensity of sound there? Solution: Substitution gives I = 3.2 x 10-5 W/m2.

16-3 Intensity of Sound: Decibels Example 16-4: Loudspeaker response. A high-quality loudspeaker is advertised to reproduce, at full volume, frequencies from 30 Hz to 18,000 Hz with uniform sound level ± 3 dB. That is, over this frequency range, the sound level output does not vary by more than 3 dB for a given input level. By what factor does the intensity change for the maximum change of 3 dB in output sound level? Solution: Call I1 the average intensity and β1 the average sound level. Then maximum intensity, I2 corresponds to a level β2 = β1 + 3 dB. Then use Eq. 16-6. Substitution shows this corresponds to a doubling or halving of the intensity.

16-3 Intensity of Sound: Decibels Conceptual Example 16-5: Trumpet players. A trumpeter plays at a sound level of 75 dB. Three equally loud trumpet players join in. What is the new sound level? Solution: The intensity has gone up by a factor of 4; the new sound level is 81 dB.