Ans. Sound waves can pass only by any medium. It cannot pass through vacuum. However, the nature of the medium will affect the speed of the sound waves. In general, the speed of sound in a liquid is five times that in gases; the speed of sound is solid is about fifteen times that in gases. The speed of sound in air is affected by changes in some physical conditions such as temperature, pressure and humidity etc. The speed of sound in solids and liquids is faster than in air.