Electromagnetic waves are ripples of electric and magnetic fields that travel through space.
Think of them like waves on a pond, but instead of water, the waves are made of electric and magnetic energy that move together.
They are transverse waves, meaning the electric (𝐸) and magnetic (𝐵) fields oscillate perpendicular to the direction of travel.
In free space, all of them travel at the same universal speed:
\$v = \frac{1}{\sqrt{\mu0 \epsilon0}} = c \approx 3.00 \times 10^8 \text{ m/s}\$
This speed is the same for radio waves, microwaves, visible light, X‑rays, and gamma rays.
The spectrum is sorted by wavelength (λ) or frequency (f). Shorter wavelengths mean higher frequencies and more energy.
| Wave Type | Wavelength (nm) | Frequency (Hz) |
|---|---|---|
| Radio | > 1 000 000 nm | < 300 MHz |
| Microwave | 1 000 – 1 000 000 nm | 300 MHz – 300 GHz |
| Infrared | 700 – 1 000 nm | 300 THz – 400 THz |
| Visible | 400 – 700 nm | 430 – 750 THz |
| Ultraviolet | 10 – 400 nm | 750 THz – 30 PHz |
| X‑ray | 0.01 – 10 nm | 30 PHz – 30 EHz |
| Gamma | < 0.01 nm | > 30 EHz |
The speed of light in vacuum, \(c\), is a fundamental constant that arises from the properties of free space: its permittivity \(\epsilon0\) and permeability \(\mu0\).
Because every EM wave obeys Maxwell’s equations, they all share the same propagation speed:
\$c = \frac{1}{\sqrt{\mu0 \epsilon0}} \approx 3.00 \times 10^8 \text{ m/s}\$
This means that whether you are looking at a radio broadcast or a gamma‑ray burst, the wave fronts move at the same speed once they are in a vacuum.
Imagine plucking a guitar string. The string vibrates up and down, perpendicular to its length.
Similarly, in an EM wave, the electric field oscillates in one direction, the magnetic field in a perpendicular direction, and both are perpendicular to the direction the wave travels.
This is what we call a transverse wave.