# Is Color a Physical Property

The physical properties of a substance actually help you describe the nature and state of matter. Color is one of the nature of matter, so is color a physical property?

Color is a property of a substance. Rather it is perceived as a sensation. In most cases, the color of the substance does not react with the other substance; Thus, color is considered a physical property.

The color of an object can be seen and measured. The color of an object comes from the reflection of light on the surface that is illuminate on it. The entire phenomenon of color is cause by the absorption, reflection or emission of electromagnetic spectra on the surface of the object, and therefore color is a physical property.

## How is color a physical property?

When a substance absorbs light of a particular wavelength from the spectra and the remaining wavelength is reflected off the surface, the reflected wavelength gives the color for that material.

When determining the color of a material, it does not cause any change in structure or react with other materials to form a new compound. Light wave has only absorption and reflection and hence exhibits physical properties.

For better understanding, assume that a band of the color spectrum falls on the material, which absorbs wavelengths of 540 and 460 nm and reflects wavelengths of 680 nm. The resulting color of the material is red because the wavelength of red is 700-635nm. The absorbed colors are green and blue because the wavelength of green is 560-520nm and blue is 490-450nm. Since green and blue are absorbed by the material and red is reflected, the composition of the material does not change; Therefore color is a physical property of the material.

## Is a change in color a physical property?

In the previous section, we described color as a physical property, but we are still unaware of whether a change in color is a physical property . We can get the answer by considering fade out material color as an example.

If you consider your fabric, some fabrics tend to discolor and bleed through their dye and lose color. It is nothing but a change in colour. Even if the color fades, the structure of the fabric remains unchanged; The cotton cloth remains as a cotton cloth; Even after the color fades, it does not become silk or nylon fabric. Since the change in color does not affect the structure of the material, the change in color is a physical property.

## How is a change in color a physical property?

Color change is the most efficient way to specify the occurrence of change in attributes. To specify a change in color as a physical property, let’s consider the following examples.

• Copper(II) hydroxide is in blue; If you heat a solution of copper hydroxide, eventually you will get a black solution of copper oxide. Here a chemical reaction has taken place, which is indicated by a change in the color of the solution.
• Similarly, if you mix blue or black color in water, the water becomes blue or black. It is actually a physical change as the water changes to the ink mixture without changing the composition of the ink or the water.

From the above two examples, we can say that color change is the visual perceptual nature of the material, which indicates change but does not cause change. Hence the change in color is a physical property of the material.

## Many facts need to be known

• Color is considered a physical property because it is based on properties such as absorption, reflection and emission of light spectra.
• Color is a perceptual property because it is relative to sensation and is an intuitive property of material; So we can easily differentiate colors when the spectrum of light interacts with the photoreceptor cells of our eyes.
• Humans have the ability to perceive colors in the visible light region of wavelengths from about 390 nm to 750 nm. vary up to . Above and below these wavelengths, we could not detect them.
• The visibility of color depends on the wave velocity. An object is said to have color when and only when the reflected light wave must travel at a speed of light c in a vacuum.
• What is not the only reason for the color of the object? Reflection spectra of light , but some materials undergo transmission and emission of the light spectrum, which causes the color of the material.
• Some objects that have opaque surfaces do not reflect light , but they do undergo scattering. The scattering wavelength determines the colors of such objects.
• Some object scatters all wavelengths of light with equal power; Such an object appears white, whereas an object absorbs all the wavelengths of the illuminated light, the color of such an object being black.

## Is the color an intense property or a broad property?

Suppose the property of the substance is independent of its quantity or proportion. In that case, such a property is said to be an intensive property, whereas if the property depends on the amount of substance used in the process, such a property is said to be an extensive property.

Most of the time, color is treated as an intensive property because you can differentiate the color of a matter of any shape, size or texture. But in some cases, the color also depends on the size. For example, a thin sheet of gold does not look like gold, but appears red in colour. This color difference depends on our vision and how the brain can detect it.

## Does solubility lead to color change as a physical property?

Some substances, when they are dissolved in solvent, change color; It is considered as a physical asset.

Since solubility is also a physical property, if the color of any solute dissolved in the solvent changes, then the color of the solute is a physical property. If the color of the solution is different from the color of the solution as well as the color of the solvent, a chemical reaction must occur, which is recognized by a color change; In such cases, the color change is an indicative physical property.

## What is meant by visual perception property?

The physical property of matter that specifies the interpretation of the surrounding environment is called a perceptual property.

If the property defines the view of the surrounding environment as day-time vision, night vision and twilight vision, then using the visible spectrum in the environment in which an object reflects illuminated light, the visual perception property is called .

## Is it possible for a substance to change its color by changing the temperature without affecting its physical properties?

There are some cases in which an increase or fall in temperature causes a change in color without affecting the physical behavior of the material.

Heating iron is the best example of this. When you heat an iron rod, it turns red. Iron softens, but its chemical properties, such as structure, remain the same. Even if you cool the rod, it regains its original hardness and color. So the rise or fall in temperature of the specific material does not affect the physical properties.

## Rusting of iron causes color changes; How does color change remain a physical property because rusting is a chemical process?

Iron rusts when exposed to moisture and air. Due to rusting, iron gets oxidised to give iron oxide.

When iron got rusted, the rusted place turned red. The color of the rust indicates that a chemical reaction has occurred with the iron. If you clean the rusted area with petrol, it disappears in the initial state, so the color change due to the chemical reaction is reversible.

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