Here’s how electromagnetic (EM) waves travel differently in a vacuum versus a medium:
In a Vacuum:
- Speed: Electromagnetic waves travel at the speed of light, which is approximately 3 × 10⁸ meters per second (about 300,000 km/s).
- No Medium Required: EM waves do not need a medium to travel; they propagate through the oscillating electric and magnetic fields themselves.
- No Energy Loss: Since there are no particles to interact with, the wave can travel long distances without losing energy.
- Constant Speed: The speed is constant and does not change in vacuum.
In a Medium (like air, water, glass):
- Speed Reduction: EM waves slow down compared to their speed in vacuum. The exact speed depends on the properties of the medium (like its refractive index).
- Interaction with Matter: The electric and magnetic fields interact with the charged particles in the medium. This causes temporary absorption and re-emission of the wave energy, effectively slowing the wave.
- Wavelength Changes: While frequency remains constant, the wavelength shortens because of the reduced speed.
- Possible Attenuation: The wave can lose some energy due to absorption or scattering, weakening as it travels through the medium.