Colours of Objects
Visible light has amazing colours, and our ability to see them is amazing. The human eye can recognise more than one crore of colours.
You must have seen many colours, but have you ever wondered why some objects appear red and others blue? Why does anything have a colour? The reality is that the colour of an object is just an illusion, a red object appears red because that object cannot absorb red, and that object absorbs all other colours except red. Similarly, a blue-coloured object cannot absorb only blue colour!
The 'white' light from the light source falls on that object. All colours except red are absorbed. Due to this, only red light reaches our eyes, and we see that object in red colour.
White Light and Its Constitutes
As we know that white colour is a mixture of all colours, the white coloured object does not absorb any colour, which makes it appear as white colour. Black colour is the opposite; black is not a colour in itself, it means the absence of colours. The black-coloured object still absorbs the colours, making it appear black.
If we throw such a light on a red object with all the other colours except red, then that object will appear black to us not red. Similarly, if you have noticed that the colour of clothes (or any other item) looks different in sunlight than in shop light. Here also, the reason is the same as almost all colours are present in sunlight, whereas some colours are absent in artificial light, due to which the absorption of colour by the fabric is different in both light.
The technical definition of colour would be something like this: "Colour is the visual effect produced from the spectral structure produced by the emission, distribution or reflection of light."
Scattering of Light
When light is incident on molecules, atoms and small particles, then it gets scattered in different directions. When sunlight, which is made up of seven colours, passes through the atmosphere, it is transmitted in different conditions by the particles present in the atmosphere. This is called the scattering of light.
Mirror Colour
Now, have you thought about what will be the colour of the mirror? That, too, does not absorb any colour, so its colour must also be white, shouldn't it?
A mirror is an ideal surface which gives an ideal reflection. That is, the angle of the incident ray and the reflected ray are equal. But the mirror does not absorb any colour, nor does it scatter. The colour of the light of which it is incident in the mirror reflects the light of the same colour.
A Girl Seeing Herself in a Mirror.
The colour of an ideal white paper and that of an ideal mirror are the same. But there is scattering in the white paper, it is not there in the mirror, and because of this, we see the difference in the colours of both.
Reflective Colours: Which colour reflects more light? Pure white.
Primary Colours of Light
The main colours of light are red, green and blue. In painting, red, blue and yellow are considered the primary colours, but in Physics, the primary colours are red, blue and green. Those colours of light cannot be obtained by mixing any other colours and are independent. They are called primary colours or basic colours. There are three primary colours of light - Red, Green, and Blue. These are denoted by 'RGB'.
Other colours are formed by mixing these three colours of light. Those colours of light that are not independent in themselves, and are obtained by mixing two primary colours are called secondary colours.
Solved Questions
1. What are the main colours of light?
Ans: The main colours of light are red, green and blue.
2. What is the colour of the mirror?
Ans: The mirror does not absorb any colour, nor does it scatter. The colour of the light of which it is incident in the mirror reflects the light of the same colour.
3. When do objects appear white and black?
Ans: An object which reflects all the optical colours appears white, and that which absorbs all the colours appears black.
Learning by Doing
Kids Activity: Surfaces That Reflect Light
For this activity, we need to arrange the following materials and follow the instructions carefully.
Materials: Torch, Mirror, a box wrapped in aluminium foil, glass jar filled with water, paper and aluminium foil ball.
Instructions:
Give children access to the material.
Children will use their flashlights to shine on each material.
Children will document their observations using pictures, labels or words.
Children will conclude other surfaces that make great reflectors of light.
Summary
Light is very important in our life. Without light, we cannot see any colour in the world. In these, we have seen how we see the colours of an object.
As you know, in this chapter, we have studied many things related to light, including the topic of the scattering of light. Now, you must have understood the mirror's colour, an object's primary colours, and many other important things related to light.
FAQs on Light-Reflecting Colours
1. What determines the colour of an opaque object we see?
The colour of an opaque object is determined by the colours of light it reflects. When white light, which is a mix of all colours (VIBGYOR), shines on an object, the object's surface absorbs some colours and reflects others. For example, a red apple appears red because its surface absorbs all colours of the spectrum except for red, which it reflects back to our eyes. This principle is known as selective absorption.
2. Why does a white object appear white and a black object appear black?
An object appears white because it reflects all the colours of the visible light spectrum that fall on it, absorbing none. Conversely, an object appears black because it absorbs all the colours of light, reflecting none. Therefore, black is technically the absence of reflected light.
3. How do the primary colours of light in Physics differ from the primary colours used in painting?
The primary colours differ because one deals with additive mixing (light) and the other with subtractive mixing (pigment):
- Primary Colours of Light (Physics): These are Red, Green, and Blue (RGB). They are called additive primaries because when they are combined, they add up to create white light.
- Primary Colours of Pigment (Art): These are traditionally Red, Yellow, and Blue (though modern printing uses Cyan, Magenta, Yellow, and Black - CMYK). They are subtractive because pigments absorb light. Mixing them subtracts more colours from the white light, and combining all three produces a dark, muddy colour, not white.
4. What is scattering of light and how does it explain the blue colour of the sky?
Scattering of light is the phenomenon where light rays are redirected in various directions upon hitting small particles like atoms, molecules, or dust in the atmosphere. The sky appears blue because the tiny molecules of air in the Earth's atmosphere scatter shorter-wavelength light, like blue and violet, more effectively than longer-wavelength light, like red and orange. Since our eyes are more sensitive to blue light, the scattered blue light reaches our eyes from all directions, making the sky appear blue.
5. Why would a green leaf appear black if viewed under a pure red light?
A green leaf appears green because it reflects green light and absorbs other colours. If you view it under a pure red light, there is no green light for the leaf to reflect. The leaf's surface will absorb the red light that falls on it. Since no light is reflected back to the observer's eye, the leaf will appear black. This demonstrates that an object's perceived colour depends on both its surface properties and the colour of the light illuminating it.
6. If a perfect mirror reflects all colours, why does it look different from a white sheet of paper?
While both a white sheet of paper and a perfect mirror reflect all colours of light, they do so differently. A mirror has a very smooth surface that causes specular reflection, meaning it reflects light rays at the same angle they arrive, creating a clear image. A white sheet of paper has a rough surface that causes diffuse reflection, scattering the light rays in all directions. This scattering is why the paper appears white and opaque, rather than forming a reflective image like a mirror.
7. What is the dispersion of light, and what is its most common real-world example?
Dispersion of light is the splitting of white light into its seven constituent colours (Violet, Indigo, Blue, Green, Yellow, Orange, and Red - VIBGYOR) when it passes through a transparent medium like a glass prism. This happens because the angle of refraction is slightly different for each colour. The most common and spectacular example of dispersion in the real world is the formation of a rainbow, where tiny water droplets in the atmosphere act as prisms to split sunlight into its spectrum of colours.
