Test: Waves - Mechanical Engineering MCQ

 When a pebble is thrown in still water, a circular pattern of alternate crests spread out. The kinetic energy makes the particles to oscillate which comes in contact with it. The energy gets transferred to the particles of next layer which also begins to oscillate. Thus it is the disturbance or waves that move forward and not the particles of the medium.

Waves which require a medium for their propagation are called mechanical waves. They are also called elastic waves because they depend on the elastic properties of medium.

The friction force amongst the particles of the medium should be negligibly small so that they continue oscillating for a sufficiently long time and the wave travels a sufficiently long distance through the medium

Transverse waves travel in the form of crests and troughs. They involve changes in shape of the medium. So they can be transmitted through media which have rigidity. As fluids do not sustain shearing stress, transverse waves cannot be formed in them.

Longitudinal waves involve changes in volume and density of the medium. Since all media can sustain compressive stress, longitudinal waves can be transmitted through all the three types of media.

Speed = √(Ƞ/ƿ)
Speed = 2.79×10³ m/s

The compressions and rarefactions are formed so rapidly that the heat generated in the regions of compressions does not get time to pass into the regions of rarefactions so as to equalise the temperature. So when sound travels through gas, the temperature remains constant. Therefore, it is adiabatic.

 When two identical longitudinal waves travelling in opposite directions overlap, a longitudinal stationary wave is formed. Thus, the waves produced in organ pipes are longitudinal stationary waves.

When a wave travels from one medium to other, its wavelength as well as velocity may change. This is the reason that frequency is the fundamental property of wave.

Sound travels in solid with highest speed because the coefficient of elasticity of solids is much greater than the coefficient of elasticity of liquids and gases.