Question

Speed of electromagnetic waves is the same:
A. For all wavelengths
B. In all media
C. For all intensities
D. For all frequencies

Answer 1

Hint: Light waves are a form of electromagnetic radiation. We will use the concepts of speed of light in different mediums and its relationship with different wavelengths and frequencies. Intensity of an electromagnetic wave is the number of photons travelling per unit time per unit cross section area on which it gets incident.

Complete step by step answer:
Light wave is an electromagnetic wave. The speed of light in vacuum is constant and there is no velocity found which is greater than this velocity. Now, the speed of light or an electromagnetic wave is dependent upon the medium through which it travels in the following way;
\[v = \dfrac{c}{n}\]
Here, v is the velocity of the electromagnetic wave travelling in the medium, c is the speed of light in vacuum and n is the refractive index of the material or the medium. Now, the speed of light or an electromagnetic wave also depends upon the frequency and the wavelength as per the formula given below;
\[c = f\lambda \]
Here, c is the speed of light in vacuum; f is the frequency of the light and \[\lambda \]is the wavelength of the light. Hence the speed of electromagnetic waves depends both on frequency and wavelength. The speed of light is only independent of the intensity.

Hence, option C is the correct answer.

Note:When electromagnetic waves are passing through a medium, then their speed decreases. The denser the medium more would be its refractive index and hence its speed would be more decreasing. In spite of having different wavelengths, all sorts of waves such as microwaves, X-rays will travel with the same speed because of different frequencies.