Question 65
1. In a seismograph, P waves are recorded earlier than S waves.
2. 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.
Which of the statements given above is/are correct?
AOptions
BSolution
Let's analyze the statements regarding seismic waves:
1. In a seismograph, P waves are recorded earlier than S waves. This statement is correct. P-waves (Primary waves) are compressional waves that travel through solids, liquids, and gases. They are the fastest seismic waves. S-waves (Secondary waves) are shear waves that can only travel through solids and are slower than P-waves. Consequently, P-waves are always the first to arrive and be recorded by a seismograph after an earthquake.
2. 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. This statement is correct. This accurately describes the nature of P-waves as longitudinal waves (particle motion is parallel to wave direction, causing compression and rarefaction) and S-waves as transverse waves (particle motion is perpendicular to wave direction, causing shaking or shearing).
Both statements are correct.
CStrategy
For questions on seismic waves, remember the basic properties of P and S waves: their relative speeds, their ability to travel through different media, and the nature of particle motion. These are fundamental concepts in seismology and Earth's interior studies.
DSyllabus Analysis
This question falls under 'Physical Geography - Geomorphology' and 'General Science - Physics' in the UPSC Prelims syllabus, specifically focusing on the internal structure of the Earth and seismic waves.
EQuestion Analysis
Easy to Medium. These are fundamental concepts related to seismic waves that are widely covered in geography and general science curricula.