Question

Which of the following is not a longitudinal wave?
(A) Seismic P-wave
(B) Light
(C) Sound
(D) Ultrasound

Answer 1

Hint: A longitudinal wave is a wave whose direction of propagation is parallel to the direction of the vibration of the particles of the source. We need to investigate how the waves in the options are generated and propagated.

Complete step by step solution:
In general, there are two types of wave based on their direction of propagation with respect to their source. One is the longitudinal wave and the other is the transverse wave
The longitudinal wave is a kind of wave whose direction of vibration of the particle is parallel to the direction of propagation of the wave. This is to that, when the molecules of the source are vibrating in, say, the $ x $ axis, then the wave is also propagating on the $ x $ axis.
The seismic wave is a wave which propagates in the earth as a result of earthquakes, volcanic eruptions and other disturbances in the earth. It is a longitudinal wave. Other longitudinal waves include sound and ultrasound (which is actually sound too)
Transverse wave – this is a type of wave in which its direction of propagation is perpendicular to the direction of vibration of the particles of the source. This is to say that, if the particles of the source are vibrating on the $ y $ axis, then the wave would be propagating on the $ x $ axis and/or on the $ z $ axis. A few examples of transverse waves are electromagnetic waves, such as light, radio waves, etc.
Hence, the correct option is B.

Note:
For clarity, these types of waves are classified based on their mode of propagation with respect to their source particles. One other classification is based on whether it requires a material medium or not. Which is classified as mechanical waves (requires material medium) and electromagnetic waves (do not require material medium).