Question

The speed of electromagnetic waves in a vacuum depends upon the source of radiation. It

• A. increases as we move from γ-rays to radio waves
• B. decreases as we move from γ-rays to radio waves
• C. is the same for all of them
• D. None of the above

Answer 1

The correct option is C

is the same for all of them

1. The speed of electromagnetic waves in a vacuum is given by $c=\frac{1}{\sqrt{{\mu }_o{\epsilon }_o}}$where $c$ is the speed of light whose value is constant as $3\times {10}^8\mathrm{m}/\mathrm{s}$ and ${\mu }_o$ is the permeability and permittivity of free space.
2. Also, from the formula speed of light is given by $Speed\left(c\right)=Frequency\left(f\right)\times Wavelength\left(\lambda \right)$.
3. The electromagnetic field's waves, which are conveying electromagnetic radiant energy through space, are what make up electromagnetic radiation.
4. As we move from gamma rays to radio waves and their wavelength increases and the frequency steadily drops. As a result, the frequency-wavelength product will never change.
5. Thus, the speed of electromagnetic waves in a vacuum is the same for all of them.

Hence option C is the correct answer.