Consider the following statements: 

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?
(a) 1 only
(b) 2 only
(c) Both 1 and 2
(d) Neither 1 nor 2

The correct answer is (c) Both 1 and 2.

Explanation:

1. In a seismograph, P waves (Primary waves) are recorded earlier than S waves (Secondary waves). This is correct because P waves are faster than S waves and so, reach the recording instrument first.
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 is also correct. P waves are compressional or longitudinal waves, which means the ground particles move in the same direction as the wave. In contrast, S waves are transverse waves, meaning the ground particles move perpendicular to the direction of wave propagation.

Inputs from Geography Mindmap Notes