Question

Elastic waves in solid are
A. Transverse
B. Longitudinal
C. Either transverse or longitudinal
D. Neither transverse nor longitudinal

Answer 1

Hint: In solids, elastic waves occur in two forms. Primary waves during the earthquake are examples of longitudinal elastic waves. Secondary waves during the earthquake are examples of transverse elastic waves.

Complete step-by-step answer:
An elastic wave is the propagation of disturbance through a solid, liquid or a gaseous medium. During this propagation, the energy of the elastic deformation gets transferred even in the absence of flow of matter. The acoustic wind is an example of this. An elastic wave can be a plane, spherical or cylindrical wave. The elastic waves have a special property, that is its phase and group velocities are independent of wave amplitude and wave geometry.
Two types of elastic waves are possible in solids. The longitudinal and shear or transverse waves. In longitudinal waves, the wave propagation and the motion of the particles will be in a parallel direction. The deformation happening due to the longitudinal elastic waves will be the sum of uniform compression or extension and shear. In transverse waves, the particle motion will be perpendicular to the direction of wave propagation. Here the deformation happens only due to the shear.
During elastic waves, stress is proportional to the strain since they obey Hooke’s law. If the strain is larger due to the wave, then the stress exceeds the elastic limit of a substance. So plastic deformation will occur. These waves can be called elastoplastic. If we are dealing with liquid or gas, these types of waves are called a finite-amplitude wave.
The correct option is C.

Note: During an earthquake, you can feel transverse as well as longitudinal waves. It reaches to us as secondary and primary waves respectively. Primary waves will travel faster and secondary waves will travel slower. In liquids and gases, only longitudinal elastic waves are present. These waves are elastic concerning the volume but not with the shape. That’s why transverse waves are not possible for liquids and gases.