1.3 Introduction
1.3.1 Characteristics of Sound - Pressure Variations
1.3.2 Characteristics of Sound - Speed of Sound
1.3,3 Characteristics of Sound - Pitch Loudness and Timbre
1.3.4 Characteristics of Sound - Intensity
1.3.5 Doppler Effect
Unit 2.1 Multiple Choice Extended Questions - Waves
Unit 2.1 Multiple Choice Extended Answers-Waves
Unit 1.3 Multiple Choice Questions - Sound
Unit 1.3 Multiple Choice Answers - Sound

Unit 1.3 Sound Waves

musical instruments dance.jpg
Painting of musical instruments in an Ecuador museum
Traditional Dance outside the Cathedral of Granada, Nicuragua

So far we have looked at waves which move:

1. in one dimension like the waves on strings in musical instruments or a rope
2. in two dimensions like the waves on the surface of a pond

We will look at waves in a three dimensions, specifically sound waves. It is true that sound waves travel through any medium 9solid, liquid or gas), but most of our analysis will be concentrated on sound waves in air as it is obvious that hearing is a direct result of these effects.

Question: When a wave from a vibrating string or surface disturbs the air and propagates itself, which (if any) characteristics of the sound waves are changed?

A. Speed (hint... does the nature of a medium affect the speed of a mechanical wave?)

B. Frequency (hint... if you put your ear against a wave traveling in say a solid medium, would the frequency change if you listened at the same sound as it leaves the solid and enters the air?)

C. Period (hint...consider the relationship between period and frequency)

D. Wavelength (hint... consider the equation v = fλ)

Recall that sound waves are mechanical waves and obey the rules of mechanical sinusoidal waves...

There are three categories of sound waves and it should be no surprise that they are based on the range of human hearing.

1. Audible (20 -20000 Hz) - range of sensitivity of the best human ear. Musical instruments, human voices, loudspeakers moving objects produce these.

2. Infrasonic - below the audible range. Infrasonic waves are produced by large animals like whales (in water) and elephants (in air) for long distance communication.

3. Ultrasonic waves - above the audible range. Animals like dogs can hear in this range ('silent dog whistle) and everyone is familiar with ultrasonic medical imaging.

We now move on to the characteristics of sound waves...

Concept by Kishore Lal. Programmed by Kishore Lal... Copyright © 2015 Kishore Lal. All rights reserved.