1. Speed of sound in different materials…
  2. V = (B/r)(1/2)
  3. Where B = bulk modulus and r = density (mass/volume)
    Material Bulk Modulus Density
    Iron, cast 90 x 109 N/m2 7.8 x 103 kg/m3
    Steel 140 x 109 N/m2 7.8 x 103 kg/m3
    Granite 45 x 109 N/m2 2.7 x 103 kg/m3
    Water 2.0 x 109 N/m2 1.0 x 103 kg/m3
    Alcohol 1.0 x 109 N/m2 0.79 x 103 kg/m3

    Ques: Calculate the speed of sound waves (these are longitudinal waves) in Granite and in Alcohol…

    Ans: look up the bulk modulus and density for each of these substances…

    Vgranite = (45 x 109 N/m2/2.7 x 103 kg/m3)(1/2)

    Vgranite = 4082 m/s

    You can try alcohol using the table info above….

  4. Intensity (decibels - dB)
  5. a)Find the decibel level for an intensity of 4.5 x 10-6 watts/m2?
  6. Use b = 10 log(I/[1 x 10-12])

    b = 10 log([4.5 x 10-6]/[1 x 10-12])

    b = 10 log(4.5 x 106)

    b = 10 (6.65)

    b = 66.5 dB

    b)A decibel level of 75 dB is measured. What intensity is this?

    75 dB = 10 log(I/[1 x 10-12])

    7.5 = log(I/[1 x 10-12])

    107.5 = (I/[1 x 10-12])

    (1 x 10-12) 107.5 = I

    I = 3.16 x 10-5 W/m2