Multiple Choice Questions
Q.1. Water waves produced by a motor boat sailing in water are
(a) Neither longitudinal nor transverse.
(b) Both longitudinal and transverse.
(c) Only longitudinal.
(d) Only transverse.
Water waves produced by a motorboat sailing on the surface of deep water are both longitudinal and transverse because the waves, produce transverse as well as lateral vibrations in the particles of the medium. The water molecules at the surface move up and down; and back and forth simultaneously describing nearly circular paths as shown in Figure.
As the wave passes, water molecules at the crests move in the direction of the wave while those at the troughs move in the opposite direction.
Q.2. Sound waves of wavelength λ travelling in a medium with a speed of v m/s enter into another medium where its speed is 2v m/s. Wavelength of sound waves in the second medium is
Frequency remains unchanged in both the medium.
λ1 and λ2 are wavelengths and v1 and v2 are speeds in first and second medium respectively.
Hence the wavelength of sound waves in the second medium is 2λ.
Q.3. Speed of sound wave in air
(a) Is independent of temperature.
(b) Increases with pressure.
(c) Increases with increase in humidity.
(d) Decreases with increase in humidity.
We know that speed of sound in air is given by
for air γ ans P are constants.
where ρ is the density of air.
where ρ1 is density of dry air and ρ2 is density of moist air. Dur to the presence of moisture, density of air decreases.
Hence, speed of sound wave in air increases with increase in humidity.