Question

The speed of electromagnetic waves in vacuum is

• A. \(30\times10^8\ \text{ms}^{-1}\)
• B. \(4\times10^8\ \text{ms}^{-1}\)
• C. \(3.0\times10^8\ \text{ms}^{-1}\)
• D. \(3.0\times10^9\ \text{ms}^{-1}\)

Hint:

All electromagnetic waves travel in vacuum with speed: \[ c=3.0\times10^8\ \text{m/s} \]

Answer 1

The Correct Option is C

Concept:
Electromagnetic waves are waves made up of oscillating electric and magnetic fields. Examples include: \[ \text{Radio waves, microwaves, infrared rays, visible light, ultraviolet rays, X-rays and gamma rays} \] All electromagnetic waves travel with the same speed in vacuum. This speed is equal to the speed of light: \[ c=3.0\times10^8\ \text{m/s} \]

Step 1: Recall Maxwell's result.
According to electromagnetic theory, the speed of electromagnetic waves in vacuum is: \[ c=\frac{1}{\sqrt{\mu_0\varepsilon_0}} \] where, \[ \mu_0=\text{permeability of free space} \] \[ \varepsilon_0=\text{permittivity of free space} \] The numerical value is: \[ c=3.0\times10^8\ \text{m/s} \]

Step 2: Compare with the given options.
Option (A) \(30\times10^8\) means \(3.0\times10^9\), which is too high.
Option (B) \(4\times10^8\) is not the standard value.
Option (C) \(3.0\times10^8\) is the correct speed of electromagnetic waves in vacuum.
Option (D) \(3.0\times10^9\) is also too high. Hence, the correct answer is: \[ \boxed{(C)\ 3.0\times10^8\ \text{ms}^{-1}} \]