Question

The speed of electromagnetic waves in vacuum depends upon the source of radiation. It
a. increases as we move from \[\gamma \]-rays to radio waves
b. decreases as we move from \[\gamma \]-rays to radio waves
c. is same for all of them
d. none of these

Answer 1

Hint: Speed of electromagnetic wave in vacuum is \[\dfrac{1}{{{\mu _0}{\varepsilon _0}}} = c\], where c is the speed of light.

Complete step by step solution:
We know that speed of electromagnetic wave in vacuum is given by
Speed of light = frequency $\times$ wavelength
$c=\nu \times \lambda$
= \[\dfrac{1}{{{\mu _0}{\varepsilon _0}}}\]
=constant

As we go from gamma rays to radio waves frequency decreases and wavelength increases thereby maintaining the product constant.

Therefore, option c) is the correct option.

Additional information: Electromagnetic waves are waves which can travel through the vacuum of outer space. Electromagnetic waves are created by the vibration of an electric charge. This vibration creates a wave which has both an electric and a magnetic component. An electromagnetic wave transports its energy through a vacuum at a speed of \[3.00{\rm{ }} \times {\rm{ }}{10^8}\;m/s\] (a speed value commonly represented by the symbol c). The propagation of an electromagnetic wave through a material medium occurs at a net speed which is less than \[3.00{\rm{ }} \times {\rm{ }}{10^8}\;m/s\].

Note: It is particularly important for the students to know the relation between the speed of light and the frequency of the wave. Without this very relation it is exceedingly hard to solve as there is no other relation or equation to equate the two quantities. Students also should know what happens when we move from gamma to radio waves.