Consider the following statements:

I. In a seismograph, P waves are recorded earlier than S waves.

II. In P waves, the individual particles vibrate to and fro in the direction of wave propagation whereas in S waves, the particles vibrate up and down at right angles to the direction of wave propagation.A.I onlyB.II onlyC.Both I and IID.Neither I nor II

Question

Consider the following statements: I. In a seismograph, P waves are recorded earlier than S waves. II. In P waves, the individual particles vibrate to and fro in the direction of wave propagation whereas in S waves, the particles vibrate up and down at right angles to the direction of wave propagation.

Accepted Answer

Both I and II. Statement I is correct. P waves, or primary waves, travel faster through the Earth than S waves do. Because of this speed difference, a seismograph always records the P wave first, then the slower S wave. Statement II is also correct. P waves are longitudinal waves, so particles vibrate back and forth in the same direction the wave is travelling. S waves are transverse waves instead, so particles vibrate up and down, at right angles to the wave's direction. This difference in vibration is also why S waves cannot travel through liquids, unlike P waves. So both statements genuinely hold true, making option (c) the answer.

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