UPSC CSE Prelims
Question 27
Consider the following statements :
- In a seismograph, P waves are recorded earlier than S waves.
- 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?
View correct answer and explanation
Correct answer: C
Correct Option: C (Both 1 and 2)
Explanation: P-waves are faster compressional seismic waves; S-waves are slower transverse waves whose particle displacement is perpendicular to travel direction.
Statement / Pair / Item-wise Analysis:
1. Correct/True - P-waves reach seismographs before slower S-waves.
2. Correct/True - P-waves displace particles parallel to propagation, while S-waves displace them perpendicular to propagation.
Option-wise Analysis:
A. Incorrect-omits correct item 2 (P-waves displace particles parallel to propagation, while S-waves displace them perpendicular to propagation.).
B. Incorrect-omits correct item 1 (P-waves reach seismographs before slower S-waves.).
C. Correct-exactly 2 of the 2 listed items satisfy the condition.
D. Incorrect-omits correct item 1 (P-waves reach seismographs before slower S-waves.); omits correct item 2 (P-waves displace particles parallel to propagation, while S-waves displace them perpendicular to propagation.).