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?
Detailed Explanation:
Answer: Option 3 — Both 1 and 2
Both statements are correct regarding seismic waves. P waves (Primary waves) travel faster than S waves (Secondary waves) and are therefore recorded first by seismographs. The two wave types also differ fundamentally in their particle motion characteristics.
✅ Statement 1 – Correct: P waves are indeed recorded earlier than S waves on a seismograph because they are the fastest seismic waves, traveling at speeds of 5-8 km/s in the Earth's crust compared to S waves which travel at 3-4.5 km/s.
✅ Statement 2 – Correct: P waves are compressional/longitudinal waves where particles vibrate parallel to the direction of wave propagation (to and fro motion), while S waves are shear/transverse waves where particles vibrate perpendicular to the direction of wave propagation (up and down or side to side motion).
📝 Short Notes: Seismic Waves
| Feature | P Waves (Primary) | S Waves (Secondary) |
|---|---|---|
| Speed | Fastest (5-8 km/s in crust) | Slower (3-4.5 km/s in crust) |
| Arrival Time | First to arrive | Second to arrive |
| Wave Type | Longitudinal/Compressional | Transverse/Shear |
| Particle Motion | Parallel to wave direction (push-pull) | Perpendicular to wave direction (up-down/side-side) |
| Medium | Travel through solids, liquids, and gases | Travel only through solids |
| Destructive Power | Less destructive | More destructive |
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