1. Which of the following is true about sound waves? They move faster than light.
They make wind.
They vibrate the air.
They move slower in water than in air.

They vibrate the air.

Explanation:

The sound waves in air are longitudinal while the light waves are transverse Sound wave is longitudinal because the medium particles move parallel to the direction of wave propagation, whereas a light wave is transverse because the medium particles move perpendicular to direction of wave propagation. Hence, option C is correct.

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.