1. What is the period of oscillation of the pendulum?
A pendulum bob with a mass of 30 kg is placed at the end of a string that is 1.2 m long.
What is the period of oscillation of the pendulum?
If the same mass is placed on a spring, what must the spring constant be to produced the same period of oscillation?

2. Electromagnetic Waves
AP Physics
Chapter 12

3. 12.1 Characteristics of Sound
Vibration and Waves
12.1 Characteristics of Sound

4. 12.1 Characteristic of Sound
Sound is a longitudinal wave
Caused by the vibration of a medium
The speed of sound depends on the medium it is in, and the temperature
For air, it is calculated as
12.1

5. 12.1 Characteristic of Sound
Loudness – sensation of intensity
Pitch – sensation of frequency
Range of human hearing – 20Hz to 20,000 Hz
ultrasonic – higher than human hearing
dogs hear to 50,000 Hz,
bats to 100,000 Hz
infrasonic – lower than human hearing
12.1

6. 12.1 Characteristic of Sound
Often called pressure waves
Vibration produces areas of higher pressure
These changes in pressure are recorded by the ear drum
12.1

7. 12.2 Intensity of Sound: Decibels
Vibration and Waves
12.2 Intensity of Sound: Decibels

8. 12.2 Intensity of Sound: Decibels
Loudness – sensation
Relative to surrounding and intensity
Intensity – power per unit area
Humans can detect intensities
as low as W/m2
The threshold of pain
is 1 W/m2
12.2

9. 12.2 Intensity of Sound: Decibels
Sound intensity is usually measured in decibels (dB)
Sound level is given as
I – intensity of the sound
I0 – threshold of hearing (10-12 W/m2)
– sound level in dB
Some common relative intensities
Source of Sound
Sound Level
(dB)
Jet Plane at 30 m
140
Threshold of Pain
120
Loud Rock Concert
Siren at 30 m
100
Auto Interior at 90 km/h 75
Busy Street Traffic 70
Conversation at 0.50 m 65
Quiet Radio 40
Whisper 20
Rustle of Leaves 10
Threshold of Hearing
12.2

10. Vibration and Waves
12.3 The Ear

11. A. What is the power output of the cats lungs? B. What is the relative
A cat screams at the top of his tiny lungs. If a listener 3.2 m away measures the relative intensity at 115 dB.
A. What is the power output
of the cats lungs?
B. What is the relative
intensity for a listener only
1.1 m away from the cat?

12. Steps in sound transmission
12.3 The Ear
Steps in sound transmission
12.3

13. 12.4 Sources of Sound: Strings and Air Columns
Vibration and Waves
12.4 Sources of Sound: Strings and Air Columns

14. 12.4 Sources of Sound: Strings and Air Columns
Vibrations in strings
Fundamental frequency
Next Harmonic
12.4

15. 12.4 Sources of Sound: Strings and Air Columns
Vibrations in strings
Next Harmonic
Strings produce all harmonics – all whole number multiples of the fundamental frequency
12.4

16. 12.4 Sources of Sound: Strings and Air Columns
Vibrations in an open ended tube (both ends)
Fundamental frequency
Next Harmonic
12.4

17. 12.4 Sources of Sound: Strings and Air Columns
Vibrations in open ended tubes
Next Harmonic
Open ended tubes produce all harmonics – all whole number multiples of the fundamental frequency
12.4

18. 12.4 Sources of Sound: Strings and Air Columns
Vibrations in an closed end tube (one end)
Fundamental frequency
Next Harmonic
12.4

19. 12.4 Sources of Sound: Strings and Air Columns
Vibrations in open ended tubes
Next Harmonic
Closed end tubes produce only odd harmonics
12.4

20. 12.6 Interference of Sound Waves; Beats
Vibration and Waves
12.6 Interference of Sound Waves; Beats

21. 12.6 Inteference of Sound Waves; Beats
If waves are produced by two identical sources
A pattern of constructive and destructive interference forms
Applet
12.6

22. What is the fundamental wavelength of the string?
A cat plays a guitar. The
speed of sound through
the string is 525 m/s. If
the string is 45 cm long
What is the fundamental wavelength of the string?
What is the fundamental frequency of the string.
What would be the next two harmonics produced on the string?

23. Vibration and Waves
12.7 The Doppler Effect

24. Applies to all wave phenomena
12.7 The Doppler Effect
Doppler Effect – the change in pitch due to the relative motion between a source of sound and the receiver
Applies to all wave phenomena
Objects moving toward you have a higher apparent frequency
Objects moving away have a lower apparent frequency
Doppler Effect
Light Doppler
12.7

25. If an object is stationary the equation for the wave velocity is
12.7 The Doppler Effect
If an object is stationary the equation for the wave velocity is
Sound waves travel outward evenly in all directions
If the object moves toward the observed, the waves travel at the same velocity, but each new vibration is created closer to the observer
Doppler Applet
12.7

26. The general equation is
12.7 The Doppler Effect
The general equation is
The values of Vo (speed of observer) and Vs (speed of source) is positive when they approach each other
Radar Gun
12.7