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Electromagnetic waves are a fundamental concept in physics that describe how energy can travel through space. These waves are created by the movement of electric and magnetic fields. They propagate (spread out) in all directions and do not need a medium (like air or water) to travel. This is why we can receive sunlight on Earth even through the vacuum of space.
The spectrum of electromagnetic waves covers a wide range of wavelengths and frequencies, from very long radio waves to very short gamma rays. Visible light is just a small part of this spectrum. Understanding these basics helps in grasping more specific concepts like visible light.

Wavelength and frequency are key characteristics of all waves, including electromagnetic waves. They have an inverse relationship.
Wavelength is the distance between two peaks (or troughs) of a wave. It is usually measured in meters or nanometers.
Frequency refers to how many waves pass a given point in one second and is measured in Hertz (Hz).
The higher the frequency, the shorter the wavelength, and vice versa. This relationship can be expressed with the equation:

\[ c = \lambda \cdot f \]
where:\(- c\) is the speed of light (approximately \(3 \times 10^8\) m/s),\(\lambda\) (lambda) is the wavelength, and\(f\) is the frequency of the wave.

This concept is crucial for understanding why different colors in the visible spectrum have different wavelengths and frequencies.

The visible spectrum includes all the colors of light that the human eye can perceive. When we talk about the visible spectrum, we often list the colors in two specific orders: by increasing wavelength or by increasing frequency.

Colors by Wavelength
From longest wavelength to shortest, the colors are:

• Red
• Orange
• Yellow
• Green
• Blue
• Indigo
• Violet

\(Red\) has the longest wavelength and lowest frequency, while \(Violet\) has the shortest wavelength and highest frequency.

Colors by Frequency
The reverse order applies if you list them by increasing frequency:

• Violet
• Indigo
• Blue
• Green
• Yellow
• Orange
• Red

This order highlights that \(Violet\) light waves oscillate the most frequently (highest frequency), and \(Red\) light waves oscillate the least frequently (lowest frequency).