Question

Longitudinal waves cannot travel through
A. Vacuum
B. Solids
C. Liquids
D. Gases

Answer 1

Hint: Waves come in many shapes and forms. Mechanical waves are waves that propagate through a material medium. These mechanical waves are classified into longitudinal and transverse waves. Longitudinal waves can be defined as waves in which the displacement of the medium is parallel to the direction of the propagation of the wave.

Complete step by step solution:
Longitudinal waves always need a medium to propagate. They cannot travel through a vacuum. This is because in the vacuum there is no medium in the vacuum to travel through. As longitudinal waves need a medium they cannot travel through a vacuum.
Therefore the correct option is A.

Additional Information:
Waves traveling through solid will be either transverse or longitudinal. But waves traveling through liquid or gases will be mostly longitudinal. This is because transverse waves need a relatively rigid medium to transfer their energy. As if one particle starts to move it needs to be able to pull on its nearest neighbor. But we know that in gases or liquids the particles are not solidly packed as in the case of solids so the particles will slide past each other. This sliding action which is one of the characteristics of liquids and gases prevents a particle from pulling its neighbor in a direction perpendicular to the direction of energy. It is for this reason that only longitudinal waves were observed to move in the bulk of liquids such as oceans.
Earthquakes have the capability of producing both transverse and longitudinal waves. But when seismologists study the earthquake wave they found that only longitudinal waves can travel through the core of Earth’s crusts. For this reason, they believe that the earth’s core consists mostly of liquid like molten iron.

Note:
Mechanical longitudinal waves are also called compressional waves or compressional waves. These longitudinal waves also include sound waves and seismic P-waves. An example of sound waves in a longitudinal direction is the tuning fork. The propagation speed of the sound waves mainly depends upon the type, composition of the medium, and temperature through which it propagates.