Question

Which of the following is not an electromagnetic wave?
$$\begin{gathered} (a)\text{ Radio waves} \\ \text{(b) X - rays} \\ \text{(c) Earthquake P - waves} \\ \text{(d) Gamma rays} \end{gathered}$$

Answer 1

Hint – In this question look for the option that does not lie in the electromagnetic spectrum. Every wave has its own range of frequency and wavelength in this spectra. So use the frequency and wavelength range of electromagnetic spectra to get the right option which does not lie in that region.

Complete Step-by-Step solution:
As we know that radio waves, X-rays and gamma rays all lie in the electromagnetic spectra at different frequencies and wavelength regions.
But Earthquake P – waves are not electromagnetic waves; they are known as seismic waves in seismology.
So this is the required answer.
Hence option (C) is the correct answer.

Note – Electromagnetic waves are categorized according to their frequency f or equivalently wavelength $\lambda$ as wavelength can be expressed in terms of frequency as $\lambda ={\displaystyle \frac{c}{f}}$. The frequency range of electromagnetic waves varies from ${10}^{20}to\text{ 3}\times \text{1}{\text{0}}^{11}$. Various rays coming into the categorization of electromagnetic rays are gamma-rays, x-rays, ultraviolet, visible, near-infrared, infrared, microwaves, radio waves.