Electromagnetic waves have both associated electric and magnetic fields. The electric and magnetic fields are always perpendicular to each other, and both fields are always perpendicular to the direction of propagation. The entire range of wavelengths and frequencies of electromagnetic waves is called the electromagnetic spectrum. The portion of the spectrum that can be detected by human eyes is known as the visible spectrum. Within the visible spectrum, certain wavelengths correspond to different colors. The visible spectrum ranges approximately from wavelengths of 400nm (violet light) to 700nm (red light). Violet light has a higher frequency than red light but a smaller wavelength.
In a vacuum, all electromagnetic waves travel with the same speed. This speed, designated by the constant c, is equal to
The constant c is also known as the speed of light. Since c is the speed of the wave, the relation between frequency and wavelength becomes
