Oscillations and Waves > Waves > Reflection and
Refraction
DCS# 3B35.10
FOCUSING BY
ACOUSTIC LENS
APPARATUS
function
generator/amplifier
202-17-A3
speaker
202-07-F
microphone
202-07-E1
oscilloscope
202
two balloons
202-14-D2
CO2
DESCRIPTION
Velocities of sound in air and CO2
at 0°C are 332 and 258 m/s, respectively. So CO2
has a refractive index of 1.28 for sound. A spherical balloon of
radius R has a focal length of R/0.56. An actual balloon is
ellipsoidal, so the focal length is somewhat greater. A source at
distance 2f left of the left surface is focused at distance 2f right of
the right surface.
Substitute air-filled balloon to show absence of effect.