Sarah and maria made a telephone using two cans and a string. it was a very long string. maria went upstairs in her house and sarah stayed downstairs. maria spoke softly into the can. "i can hear you! ' sarah said back. how can this happen? a)sound waves travel through a vacuum. b)sound waves travel from high to low. c)sound waves travel through solids like the string. eliminated)maria talked so loudly that sarah could hear her without the phone.

speed of light in vacuum is 300,000 km/s

speed of light in other mediums is given by the expression v = c/n, where c is the speed of light in vacuum and n is the refractive index of medium.

for the first medium v = 200,000 km/s

  so, refractive index of medium = 300000/200000 = 1.5

    1.5 refractive index is usually for glass. so first medium is glass.

for the second medium v = 250,00 km/s

so, refractive index of medium = 300000/250000 = 1.2

    1.2 refractive index is usually for water. so second medium is water.

for the third medium v = 0 km/s

so, refractive index of medium = 300000/0 = ∞

    ∞ refractive index is usually for opaque mediums. so third medium is opaque medium.