A.They alternately compress and pull apart the particles in matter.
B. They are the first waves detected after an earthquake.
Explanation:
P-waves, also known as a compressional wave is the wave that shakes the ground in the same and opposite direction of the wave i.e. back and forthe motion of the ground. They compress and pull apart the material alternatively. The disturbances due to these waves have small magnitude thus making them non destructive. These waves travel at faster speed as compared to other seismic waves and thus help in detecting the earthquake. These wave can travel through liquid, solid and gases.
It is usually expressed the other way: the ratio of the speed of light in a vacuum to the speed of light in a medium. In that case, it is called the "index of refraction".
