Light

Light: The sensation of sight helps us see the world around us. During the day, it’s the light from the sun that helps us see our surroundings, and at night it’s the light from the moon that brightens up our outside. To see, we, therefore, need a source of light. Let us read further to understand the mechanism that helps us see through our eyes.

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Laws of Reflection

Light as it falls upon a polished surface as a mirror reflects, and its direction of propagation changes. The reflection of light from a surface follows the following two laws of reflection:

1. The incident ray (the light ray that strikes a surface), the reflected ray (the light ray that comes back from the surface after reflection) and the normal (the ray making an angle of \(90^\circ\) to the ray representing the mirror at the point of incidence) to the reflecting surface all lie in the same plane.
2. The angle of incidence (the angle between the incident ray and normal) is equal to the angle of reflection ( the angle between the reflected ray and the normal).

What Makes Things Visible to Us?

We can see the things around us when the light from those things enters our eyes. The light entering our eyes may be reflected from the object’s surface or emitted from within the object itself. The light striking the object is often produced by an external source like a light, bulb, or candle. In the absence of light, we cannot see the objects around us even with our eyes open. That’s why it’s impossible to see when it’s dark.

Regular and Diffused Reflection

Reflection of light happens at almost all the surfaces at which the light falls but based on the type of surface; reflection is of two types:

1. Regular Reflection: When parallel rays of light fall on a surface after reflection, that reflection is called regular reflection. The surfaces at which the regular reflection occurs are smooth surfaces and images formed due to regular reflection on surfaces like a mirror.
2. Diffused Reflection: When parallel rays of light falling on a surface after reflection are not parallel, such a reflection is called diffused reflection. The reflection of light, even in the case of diffused reflection, follows the laws of reflection of light. The rays after reflection are not parallel because of irregularities in the surface, like cardboard.

Multiple Images

The image of an object is formed when light rays after reflection from a polished surface like a mirror meet at a certain point. If the reflected light from the first surface falls on another polished surface, this light will again get reflected. Periscopes installed in submarines, tanks and soldiers hiding in the bunkers have two plane mirrors that allow multiple reflections of light within a periscope.

To visualize this:

1. Take two pieces of plane mirrors and place them at various angles by hinging them at the centre with a piece of tape.
2. Set an angle between the mirrors and place an object between them to see how many images are formed.
3. Repeat the process for several other angles and note down the number of images formed in each case.
4. Place the two mirrors parallel to each other, and you will observe that an infinite number of images are obtained.

This phenomenon that multiple images are obtained when two or more mirrors are placed at an angle is used to design a kaleidoscope. Within the tube of a kaleidoscope, mirrors are placed at an angle with respect to each other and several sparkles and glass pieces are kept in front of the mirrors; and when it is observed from the other end of the tube, beautiful patterns are obtained. In a kaleidoscope, you will never observe a pattern more than once.

Structure of the Eye

Our eyes help us to see the world around us. Light after reflection from the surfaces enters our eyes thus, enabling us to see the world around us. We must understand the structure and working of our eyes.

Our eyes are in the shape of roughly spherical balls. Our eyes have a tough white coating on the outside, and this coat protects the inside of our eyes in case of any accidents.

Cornea

The transparent front part in front of our eyes is called the cornea.

Iris

The dark, muscular structure present behind the cornea is called Iris. It imparts colour to our eyes. When we say that a person has blue eyes, we are actually talking about the colour of their iris.

Pupil

The small opening present within the iris is called the pupil. The light from outside enters inside our eyes from this opening. Iris controls the size of the pupil and hence the amount of light entering our eyes.

Eye Lens

Light from the pupil falls on the eye lens present behind it. This lens is a convex lens that is thicker at the centre. The lens focuses on the light coming from an object and forms its image at the back of the eye.

Retina

The screen present behind the eye on which the image is formed is called the retina. It consists of many nerve cells that detect the light falling on them. There are two kinds of nerve cells present on the retina:

1. Cones: The nerve cells that are sensitive to bright light are called cones. These cells sense colour.
2. Rods: The nerve cells that are sensitive to dim light are called rods.

These nerve cells feel the sensations and then transmit them to the brain for processing.

Optic Nerve

The signals detected by the cells on the retina are transferred to the brain via the optic nerve.

Blindspot

The point where the optic nerve meets the retina, no sensory nerve cells are present. Any light falling on that spot will not be detected. Thus, there is no vision at this junction, and this spot is called the blind spot of our eye.

Persistence of Image

The image formed at the retina of our eye does not disappear immediately. It lasts on the retina for about \(\frac{1}{{16{\rm{th}}}}\) of a second. So if static images of an object are flashed in front of our eyes at a speed greater than \(16\) per second, to our eyes, it would appear as if the object is moving. Movies and TV serials are a collection of several pictures put together in a proper sequence that are displayed at a rate of \(24\) pictures per second. So to us, pictures appear to be moving.

Eyes are a sensitive organ, and that is why nature has provided us with eyelids. These eyelids protect our eyes from dust, excessive light or any other external stimuli that might cause any harm.

With our eyes, we can see distant as well as nearby objects clearly. However, the minimum distance up to which we can see comfortably varies with age. The minimum distance at which a normal human eye can read is \(25\,{\rm{cm}}\); any object kept closer to our eye, then this distance will appear blurred.

Defects of the Eye

1. Myopia: Some people can see the nearby objects clearly, but they can not see the far off objects distinctly; they are said to be suffering from myopia. This defect can be corrected using a suitable corrective lens.
2. Hypermetropia: Some people can see distant objects clearly, but they can not see the nearby objects distinctly; they are said to be suffering from hypermetropia. This defect can be corrected using a suitable corrective lens.
3. Cataract: It is observed that people complain that their eyesight has become foggy, especially as they grow old. They are suffering from cataract. Due to this, they have a loss of vision which can be extremely severe at times. It can be treated; now, with advancements in science and technology, the old opaque lens is replaced by a new artificial lens that helps the patient see clearly.

How to Take Care of Eyes?

Eyes are our camera into the world, and they need proper care and attention; in case of any issues, a person must visit an eye specialist to get their eyes properly checked. In general, keep the following few things in mind:

1. If it is recommended to you, you must always wear suitable spectacles.
2. Eyes work comfortably in suitable light; too little or too much light can cause our eyes harm.
3. It is advised to not look directly at the sun or any other powerful light.
4. If you get dust into your eyes, it is recommended to wash your eyes with water instead of rubbing them.
5. We should wash our eyes often with clean water.
6. While reading, books or phones must be kept at a suitable distance to avoid straining the eyes.

Proper functioning of eyes requires taking care of eyes not just on the outside but also on the inside, and for ensuring their health from within, a proper diet is required. Diet lacking in vitamin A can cause many eye troubles like night blindness. Thus, good sources of vitamin A must be included in our meals. Some sources of vitamin A are raw carrots, broccoli and green vegetables (such as spinach) and cod liver oil, eggs, butter, cheese, curd and fruits (papaya) etc.

Braille System

Study About Scattering of Light

Not everyone is equally gifted with sight. Some people can see the world around them clearly, but some find it difficult to see clearly. The defects in the eye may be treatable or, at times, permanent. People who suffer from partial or complete loss of vision are called visually handicapped. The loss of vision may be from birth, or it may occur later in life due to a disease or accident. Such people have other senses heightened to help them navigate through life. However, additional sources have been developed to enable their capabilities further, like the Braille system.

Lord Braille developed it in 1821, who was visually challenged himself. In 1932, the present Braille system was adopted, and it has codes for all common languages, mathematics and other important scientific notation. There are Braille codes for several Indian languages too.

Braille system is taught to visually challenge people from letters to special characters and then letter combinations, and then they have to memorize them all. These texts can be reproduced by machines like a typewriter or written by hand.

Summary

1. We can see the things around us when the light from those things enters our eyes. The light entering our eyes may be reflected from the object’s surface or emitted from within the object itself.
2. The reflection of light from a surface follows two laws of reflection: The incident ray, reflected ray and the normal all lie in the same plane, and the angle of incidence is equal to the angle of reflection.
3. Reflection, depending upon the nature of the reflecting surface, can be either regular or diffused.
4. Our eye consists of several parts like the cornea, iris, pupil, retina and optic nerve that work together to help us see the world around us. Eyes may suffer from defects due to which our vision may get compromised.
5. Braille system was developed to help visually challenged people; it has codes for all common languages, mathematics and other important scientific notation.

FAQs

Q.1. State the laws of reflection.
Ans: Laws of reflection are:
1. The angle of incidence is equal to the angle of reflection
2. The incident ray, the reflected ray, and the normal all lie in the same plane.

Q.2. What happens in the case of diffused reflection?
Ans: Diffused reflection occurs when parallel light rays after reflection from a surface are not parallel.

Q.3. What is the role of the pupil in our eyes?
Ans: The light enters our eye through the small opening in the iris called the pupil.

Q.4. What portion of our eye is responsible for colour?
Ans: The colour of the eyes is the colour of the iris.

< Q.5. Deficiency of which vitamin causes night blindness?
Ans: Yes, the deficiency of vitamin A causes night blindness.

We hope this article on Light is helpful to you. If you have any questions, related to this topic, post your comments in the comment box below and we will get back to you as soon as possible.