Post on 21-Jan-2016
PS 1-3-08
Waves and Sound
New Website address
• www.Elyceum.wikispaces.com
Time until exams
• About a week of class time towards new material
• Waves, sound, light, and maybe color
• Some graded exercise on next Wednesday
Mid-year exam
• Review next Thursday and Friday
• Find your old tests
Waves
• Interference
• Constructive interference
• Destructive interference
• Relationship between type of interference and amplitude size
Interference and bubbles
• Constructive and destructive interference creates rainbow effect on bubbles
Interference and sound
• Keeping a piano in tune
• Dead Spots in a room
Standing waves
• Occurs where at least one end of wave is fixed
• Relationship between incoming wave and reflected wave
Standing waves in guitar
Nodes
• Place along medium of complete destructive interference
• Crest of incoming cancels trough of reflected (or vice versa)
Antinodes
• Place of maximum vibration
• Constructive interference
Tacoma Narrows Bridge
• Wind created a standing wave with in structure of bridge
Homework
• Page 478
• Problems 1-6
Sound
• Type of wave
• Speed of Sound
• 331m/s @ 0°C to 386 @ 25C
• 1490-1530 C in water
• 3800-5000 C
Loudness
• Depends on the energy in the sound wave
• Intensity = rate of energy transmission through a given area of the medium
• Greater Intensity Louder sound
Measure of Loudness
• Relative intensity
• Compares the intensity of the sound with the intensity of the quietest sound that a person can hear
• Measured in decibels
Decibel scale
• 0 dB threshold of hearing
• 30 dB whispering
• 50dB normal conversation
• 70dB vacuum cleaner
• 90 dB lawnmower
• 120 dB threshold of pain
• 150 dB nearby jet airplane
Pitch
• Not related to loudness
• Related to the frequency of wave
• Humans range of hearing range from– 20 HZ to 20,000 HZ
Sound beyond human range
• Lower than 20 Hz Infrasound
• Higher than 20,000 Hz ultrasound
• Dogs can hear to 46,000 Hz
• Dolphins can hear to 150,000 Hz
Echos
• What is needed to create an echo?
Places you here an echo
Ultrasound
• Ultrasonic waves are generated and moves away from the source
• They hit an object and reflect back to the source
• The time it takes for the wave to return is recorded and used to find the distance object is from source D = v t
Example of ultrasound use
Why use ultrasonic waves?
• Focused into more narrow beams
• Directed more easily
SONAR
• Sound, Navigation, and RAnging
• Uses acoustic signals and echo returns to locate objects