Electromagnetic waves, like light, move really fast—about 300 million meters every second when they're in a vacuum.

You can figure out this speed using the formula:

$$c = \frac{1}{\sqrt{\mu_0 \epsilon_0}}$$

Here is what the symbols mean:

• $c$ is the speed of light (or electromagnetic waves).
• $\mu_0$ is a constant that represents how a magnetic field can grow in a vacuum. Its value is $4\pi \times 10^{-7} \, \text{H/m}$.
• $\epsilon_0$ is another constant that shows how an electric field can grow in a vacuum. Its value is $8.85 \times 10^{-12} \, \text{F/m}$.

When these waves travel through different materials, like water or glass, they slow down. You can calculate this slower speed with the formula:

$$v = \frac{c}{n}$$

In this formula, $n$ is called the refractive index. It tells you how much the speed of light is reduced in that material.

So, in simple terms, electromagnetic waves go super fast in space but slow down when they go through other things!