Ch 7 - Wave and Sound

Question 1

Transverse waves

Answer 1

• oscillation perpendicular to propagation

Question 2

longitudinal wave

Answer 2

• oscillate parallel to propagation
• ex. sound waves

Question 3

Superposition and Wave interference

Answer 3

• waves interact with each other the resultant is sum of displacements
• constructive interference
• destructive interference
• partially destructive or constructive

Question 4

traveling waves

Answer 4

• one end of wave is fixed
• at the end the wave is reflected
• standing waves - sum of 2 traveling waves and only movement is fluctuation in amplitude
• nodes - points that remain at rest
• antinodes - max amplitude

Question 5

Resonance

Answer 5

• natural frequency - vibrations that occur when an object is struck/tapped
• timbre - quality of sound
  
  • when vibrates at single tone, makes pure tone
• 20Hz - 20,000 Hz is audible for humans
• resonating - periodic force is equal to the natural frequency and maximizes amplitude

Question 6

Sound

Answer 6

• longitudinal wave
  
  • fastest in solid - liquid - gas slowest
  • fastest in low density solid
  • slowest in high density gas
• 343 m/s in air

Question 7

pitch

Answer 7

• perception of frequency
• infrasonic - below 20Hz
• ultrasonic - above 20,000Hz

Question 8

Doppler Effect

Answer 8

• difference between actual frequency and perceived frequency when a source of sound is moving
• moving away - lower perceived frequency
• moving towards - higher perceived frequency

Question 9

intensity and loudness

Answer 9

• intensity - average rate of energy transfer across a surface that is perpendicular to the wave
• intensity determines loudness, dependent on amplitude
  
  • squared relationship
  • double amplitude - 4x intensity
• power per unit area
• W/m²
• sound level - measured in decibels (dB)

Question 10

Standing wave

Answer 10

• nodes - no fluctuation in displacement
• antinodes - max fluctuation
• closed boundaries - no oscillation, nodes
  
  • ends of a tube
• open boundaries - max oscillation, antinodes
  
  • open end of pipe
  • non-tied end of string

Question 11

Strings

Answer 11

• length must be multiple of half the wavelength
• fixed ends are nodes
• harmonic - number of half wavelengths
• fundamental frequency - lowest frequency of a standing wave
• harmonic number is number of antinodes
  
  • only for string attached on both sides
• harmonic series - all supported frequencies

Question 12

Open pipe

Answer 12

• open pipe - open both ends
• closed pipe - closed one end
• harmonic - number of half wavelengths
  
  • in open pipe - harmonics = number of nodes

Question 13

Closed Pipe

Answer 13

• closed end - node
• open end - antinode
• harmonic = number of quarter-wavelengths
• only odd harmonics

Question 14

Ultrasound

Answer 14

• high frequency sound waves
• relies on reflection
• transmitter sends generates wave, reflects, returns to transmitter that acts as receiver