Which of the following statements with reference to L-Wave or Long Wave generated by an earthquake is/are correct? 1. They follow the Earth's circumference 2. They travel at more or less at a constant rate Select the answer using the code given below:
- (a)1 only
- (b)2 only
- (c)Both 1 and 2
- (d)Neither 1 nor 2
Correct — C, Both 1 and 2. L-waves (long or surface waves) are the last group of seismic waves recorded after an earthquake. Unlike the body waves (P and S) that pass through the Earth's interior, L-waves travel along the outer surface, so their path effectively follows the Earth's circumference (statement 1). Because they stay within the relatively uniform surface layers rather than diving through zones of changing density, they move at a more or less constant rate (statement 2). Both statements are therefore correct.
- (a)1 only — Incomplete. Statement 1 is right, but statement 2 is also correct — surface L-waves keep a roughly constant speed because they stay in the homogeneous surface layer, so limiting the answer to statement 1 alone is wrong.
- (b)2 only — Incomplete. Statement 2 is true, but statement 1 is also true — L-waves do travel along the surface, i.e. following the Earth's circumference, so leaving out statement 1 is wrong.
- (d)Neither 1 nor 2 — Both statements are actually correct, so 'neither' is wrong. L-waves both follow the surface and move at a nearly constant rate.
An earthquake radiates three main kinds of waves. Body waves travel through the Earth's interior: P-waves (primary, fastest, push-pull, pass through solids and liquids) arrive first, then S-waves (secondary, slower, side-to-side, cannot pass through liquids). Surface waves, also called L-waves or long waves, travel along the ground surface, arrive last, move slowest and cause the most damage.
The key contrast is interior vs surface travel. P and S waves cut through the deep Earth, where density changes bend and speed them up or down. L-waves instead run along the crust, so their route hugs the surface (the Earth's circumference) and their speed stays fairly steady. Recognising L-waves as the surface group makes both statements fall out naturally.
- Order of arrival at a seismograph: P-waves first, then S-waves, then L-waves last.
- L-waves (surface / long waves) travel along the Earth's surface and are the most destructive.
- P-waves pass through solids and liquids; S-waves travel only through solids.
- The instrument that records seismic waves is a seismograph; magnitude is read on the Richter scale.
- Assuming L-waves travel through the Earth's interior — they are surface waves.
- Thinking L-waves arrive first because they do the most damage — they actually arrive last and slowest.
Seismic waves are asked by property — order of arrival, medium they pass through, or which reveals the core — so learn P/S/L features side by side.
No directly related past PYQ was found.
- practice — not a real PYQ
Which seismic waves cannot pass through the liquid outer core, producing a shadow zone?
- (a)P-waves
- (b)S-waves
- (c)L-waves
- (d)All of them
Answer(b) S-waves — they travel only through solids, so their shadow zone shows the outer core is liquid.
- practice — not a real PYQ
At a seismograph, which earthquake wave is recorded first?
- (a)L-wave
- (b)S-wave
- (c)P-wave
- (d)Surface wave
Answer(c) P-wave — the primary wave is the fastest and arrives first.