Consider the following:
Statement-I: The velocity of waves changes as they travel through materials with different densities.
Statement-II: The velocity of waves decreases as the material becomes denser.
Statement-III: The direction of waves changes as they reflect or refract coming across materials with different densities.

Which one of the following is correct in respect of the above statements ?
(a) Both Statement-II and Statement-III are correct and both of them explain Statement-I
(b) Both Statement-II and Statement-III are correct, but only one of them explains Statement-I
(c) Only one of the Statements II and III is correct and that explains Statement-I
(d) Neither Statement-II nor Statement-Ill is correct

Question

Consider the following:
Statement-I: The velocity of waves changes as they travel through materials with different densities.
Statement-II: The velocity of waves decreases as the material becomes denser.
Statement-III: The direction of waves changes as they reflect or refract coming across materials with different densities.

Which one of the following is correct in respect of the above statements ?
(a) Both Statement-II and Statement-III are correct and both of them explain Statement-I
(b) Both Statement-II and Statement-III are correct, but only one of them explains Statement-I
(c) Only one of the Statements II and III is correct and that explains Statement-I
(d) Neither Statement-II nor Statement-Ill is correct

ONLiNE UPSC · Accepted Answer

The velocity of waves changes as they travel through materials with different densities because seismic wave velocity depends on the properties of the material, such as density and elasticity. Earthquake waves are basically of two types: Body waves and Surface waves. Body waves are generated due to the release of energy at the focus and move in all directions travelling through the body of the earth. Hence, the name body waves. The body waves interact with the surface rocks and generate new sets of waves called surface waves. These waves move along the surface.

Statement II is not correct: The denser the material, the higher is the velocity. Seismic velocities depend on the material properties such as composition, mineral phase and packing structure, temperature, and pressure of the media through which seismic waves pass. Seismic waves travel more quickly through denser materials and therefore generally travel more quickly with depth.

Statement III is correct: The direction waves also change as they reflect or refract when coming across materials with different densities.

Statement III is correct and explains why wave velocity and direction change across materials of different densities.

Wave Mechanics

Velocity and Direction of Waves in Different Materials

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M Question 1	⏱ 0
Consider the following: Statement-I: The velocity of waves changes as they travel through materials with different densities. Statement-II: The velocity of waves decreases as the material becomes denser. Statement-III: The direction of waves changes as they reflect or refract coming across materials with different densities. Which one of the following is correct in respect of the above statements ? (a) Both Statement-II and Statement-III are correct and both of them explain Statement-I (b) Both Statement-II and Statement-III are correct, but only one of them explains Statement-I (c) Only one of the Statements II and III is correct and that explains Statement-I (d) Neither Statement-II nor Statement-Ill is correct