How did Newton show that a prism breaks white light into its component colors, but does not add any color to the light?

When Sir Isaac Newton first passed a beam of sunlight through a glass prism, he witnessed what we now call the dispersion of light. This process occurs when light enters the prism and splits into an array of individual colors. This happens because light is composed of waves with varying wavelengths. Different wavelengths bend by different amounts when they pass through a substance like glass. The varying bending, known as refraction, causes each color to spread out into a separate band.

In simple terms, think of white light as a crowd of people running through a gate (the prism). As they pass through, each person takes a slightly different path—it's as if they’re racing on tracks that bend distinctively depending on their running speed. This race leads them to fan out, creating a spread—much like how light rays spread out to form the spectrum.

The visible spectrum, fondly remembered by the mnemonic 'ROYGBIV' (red, orange, yellow, green, blue, indigo, violet), is essentially the part of the electromagnetic spectrum that human eyes can perceive. Newton's prism experiment illustrated that white light is a blend of these colors. When white light disperses, each color appears at a specific position, red being on one end (least refracted) and violet on the other (most refracted).

Think of the spectrum as a team of colors where everyone has their unique position in the lineup. These positions are based on their wavelength; red light has the longest wavelength and violet light has the shortest. This is why a rainbow is always color-ordered in the same way, creating a natural spectrum in the sky.

Refractive properties refer to how light changes direction, or refracts, when moving between different mediums. In Newton's experiment, when light passed from air into the glass prism, it changed speed due to the difference in density between air and glass. This change in speed resulted in a change of direction, an effect known as refraction.

Each color in the spectrum has a particular refractive index, which is a measure of how much it can bend. A simple analogy would be different swimmers who change lanes when moving from one density of water to another. Blue light bends more than red because it 'swims' differently in the 'glass water'. Newton's clever second-step, with the inverted prism, demonstrates that we can reverse the effect, proving that the properties of refraction are inherent to light itself, not something that the prism contributes.