What is mirage or optical illusion?

What is mirage or optical illusion?

PROF WAQAR HUSSAIN

          

                

          Mirage or optical illusion is a naturally occurring optical phenomenon in which observer sees water and 

inverted images of distant object that disappear on reaching near the spot.In contrast to hallucination, it is real phenomenon which can be captured in camera.Meaning of word mirage is " to look at".  In order to understand the phenomenon of mirage, first have a clear concept of total internal reflection. When, a beam of light passes from a denser to a rare medium, refracted ray bends away from the normal and the  

angle of refraction is greater than the corresponding angle of incidence. As the angle of incidence increases, the angle of refraction also increases till for a certain value of angle of incidence, the corresponding angle of refraction equal to 90⁰ .The angle of incidence for which the angle of refraction is 90⁰ is called the critical angle.

           When the value of angle of incidence becomes greater than the critical angle, the ray of light no longer suffers refraction but the whole of it, is reflected back in the denser medium. Such a reflection of light is called total internal reflection.

            

       Mirage is good example of total internal reflection. In desert during the hot day time the travelers often see distant pool of water and inverted image of trees in it.  On reaching this  

spot they see nothing but hot sand. This is an optical illusion and is known as mirage. Mirage is generally seen on road surfaces in hot season or in hot desert.

     In desert sand becomes very hot during the day time and the air, in contact with it, is heated and becomes rarer as compared to the layers of air above it. Thus as we go up, the layers of air go on becoming denser.

       The rays of light travelling downward from the top of a tree pass continuously from denser to rarer layers of air and are thus refracted away from the normal. Finally these rays meet a surface of a layer of air with angle of incidence greater than the critical angle and suffer total internal reflection. These rays are thus directed upward. If these reflected rays enter the eye of a traveler, an inverted image of the tree is seen and the hot sand appears like a lake of water. However this phenomenon is called an optical illusion.

Why on hot days, we see water on the distance place and it disappears when we go nearby it?

Why on hot days, we see water on the distance place and it disappears when we go nearby it?

PROF WAQAR HUSSAIN

           

MIRAGE OR OPTICAL ILLUSION IN DESERT      

                 

                In order to understand the phenomenon of mirage, first have a clear concept of total internal reflection. When, a beam of light passes from a denser to a rare medium, refracted ray bends away from the normal and the angle of refraction is greater than the corresponding angle of incidence. As the angle of incidence increases, the angle of refraction also increases till

for a certain value of angle of incidence, the corresponding angle of refraction equal to 90⁰ .The angle of incidence for which the angle of refraction is 90⁰ is called the critical angle.

           When the value of angle of incidence becomes greater than the critical angle, the ray of light no longer suffers refraction but the whole of it, is reflected back in the denser medium. Such a reflection of light is called total internal reflection.

             Mirage is good example of total internal reflection. In desert during the hot day time the travelers often see distant pool of water and inverted image of trees in it.  On reaching this spot they see nothing but hot sand. This is an optical illusion and is known as mirage. Mirage is generally seen on road surfaces in hot season or in hot desert.

    

In desert sand becomes very hot during the day time and the air, in contact with it, is heated and becomes rarer as compared to the layers of air above it. Thus as we go up, the layers of air go on becoming denser.

       The rays of light travelling downward from the top of a tree pass continuously from denser to rarer layers of air and are thus refracted away from the normal. Finally these rays meet a surface of a layer of air with angle of incidence greater than the critical angle and suffer total internal reflection. These rays are thus directed upward. If these reflected rays enter the eye of a traveller, an inverted image of the tree is seen and the hot sand appears like a lake of water. However this phenomenon is called an optical illusion.

Why we sees different colour in rainbow?

Why we sees different colour in rainbow?

 PROF WAQAR HUSSAIN  

       

     When sun rays fall on a drop of water hanging in the sky, they are split up into seven constituent colours; Violet, Indigo, Blue, Green, Yellow, Orange and Red. A rainbow is thus formed by combined refraction, dispersion and internal reflection of sun’s rays on rain drops.

     The light is first refracted as it enters the surface of the raindrop, then reflected off the back of the drop, and again refracted as it leaves the drop.

The incoming light is reflected back over a wide range of angles, with the most intense light at an angle of 40°–42°. The angle doesn’t depend on the size of the drop, but on its refractive index.

The rain drops act like so many glass prisms splitting up the sunlight which enters them. When infinite number of rays strike a number of droplets they form arc of a circle and are called the rainbow. Rainbow is seen when the sun is at the back of the observer and sun rays fall on the tiny drops in front.

Why prisms disperse light into seven colours?

Why prisms disperse light into seven colours?

PROF WAQAR HUSSAIN

        

         When white light passes through a prism, the different colours are refracted differently. Light of particular colour is refracted in a direction  different than light of any other colour As the refraction of light of each colour is different, so white light after passing through a prism is separated into different colours. Separation of white light into its constituent colours is called dispersion of light.

        We know that the speed of light changes as it passes from one medium to another. The decrease in the speed of the violet light is maximum when it passes from air to glass, while the speed of red light is decreased the least. That is why the violet light is bent the most and red light the least.

        

         Red light has the largest wavelength (the distance between two adjacent crests and troughs) and the violet light has the smallest wavelength. On passing through a prism, a radiation of longer wavelength is bent to a smaller degree and radiation of smaller wavelength is bent to a greater degree. Thus every colour bends differently according to its wavelength and separate. Let’s have an analogous example, red has large wavelength like the stride of a large man and violet has a small wavelength like a small kid. When, red light and violet light pass through a curved hurdle of prism; red bends the least and violet the most. Likewise if a brick is placed on the way of man and kid, the large stride man will experience fewer hurdles , his speed will reduce a little and thus his walking posture will bend slightly as compared to small stride kid who will experience greater hurdle, his speed will reduce more and his walking mode will bend greatly. Similarly long stride red bends less and short stride violet bends too much.

What causes an object to look red or green, etc?

What causes an object to look red or green, etc?

PROF WAQAR HUSSAIN

         When light falls on a red object, it absorbs all radiations except red. So red wavelength is reflected back and the thing appears red. For example, a tomato looks red as it absorbs all wavelengths of colours i.e. violet, indigo, blue, green, yellow and orange except red and thus red is reflected and tomato appears red.

          Similarly a green chilli absorbs all the colours except the green which is reflected back and it appears green. So you can make a general formula that the colour of the thing is the colour it is reflecting.

Why red colour cloth is used in bullfighting?

PROF WAQAR HUSSAIN

                 

    Bullfighting didn’t begin in Spain as many people believe today. This illusion is probably for the reason of too much affection and craze of Spanish for the bullfighting. The sport originated in ancient Mesopotamia and the areas around the Mediterranean.

            In bullfighting, an angry, fuming and infuriated bull charges at a matador’s small red cloth (muleta).  Most believe that the bull irritates and charges at the sight of red colour!

            It is a mistaken misconception; in fact, bull, is colour blind to red like all other cattle. In fact, the bull is not irritated by the muleta’s red colour, but by the cape’s movement when the matador whips it around.

             A research, conducted by Discovery Channel in 2007, proved the above conclusion. In the TV Program, three live tests were shown which confirmed the choice of bull between colour and movement.

             Experiment No 1:  Three stationary flags of red, blue and white colours were placed in the bull’s enclosure. The bull charged on all the three flags irrespective of colours. (It means bull’s charge in independent of the colour).

             Experiment No 2: Three dummies dressed in red, blue and white were placed in the ring. The bull charged on all the three dummies regardless of their colours. Surprisingly, the bull charged the red dummy last. (It means bull’s charge doesn’t instigated by the colour).

              Experiment No 3: Three  persons were stationed in the ring; one person who was dressed in red, stood still while the other two were dressed in colours other than red but were   moving in the ring. The bull attacked the moving persons and left the motionless person wearing red clothing. (It means bull’s attack is not prompted by red colour).

              Conclusion is crystal clear; the bull is annoyed by the movement and not by red colour. Thanks to Discovery Channel which solved the sphinx riddle and helped us to reach the real cause of bull’s outrage.

             

           Still one question is irritating, if red colour is not irritating then why the muleta of red colour is used? The answer is: It is a concealing tactic; in the last stage of the bullfighting, when the bull meets its end, a dagger is run through in a way to hit bull’s heart and hence red colour rag helps to mask one of the horrible and terrifying aspects of bullfighting i.e. “the concealing of bull's blood”.

Astonishing Fact Revealed: In bullfighting, Bull charges at moving things instead of red colour!

 

PROF WAQAR HUSSAIN

   

Bullfighting didn’t begin in Spain as many people believe today. This illusion is probably for the reason of too much affection and craze of Spanish for the bullfighting. The sport originated in ancient Mesopotamia and the areas around the Mediterranean.

            In bullfighting, an angry, fuming and infuriated bull charges at a matador’s small red cloth (muleta).  Most believe that the bull irritates and charges at the sight of red colour!

            It is a mistaken misconception; in fact, bull, is colour blind to red like all other cattle. In fact, the bull is not irritated by the muleta’s red colour, but by the cape’s movement when the matador whips it around.

             A research, conducted by Discovery Channel in 2007, proved the above conclusion. In the TV Program, three live tests were shown which confirmed the choice of bull between colour and movement.

             Experiment No 1:  Three stationary flags of red, blue and white colours were placed in the bull’s enclosure. The bull charged on all the three flags irrespective of colours. (It means bull’s charge in independent of the colour).

             Experiment No 2: Three dummies dressed in red, blue and white were placed in the ring. The bull charged on all the three dummies regardless of their colours. Surprisingly, the bull charged the red dummy last. (It means bull’s charge doesn’t instigated by the colour).

              Experiment No 3: Three  persons were stationed in the ring; one person who was dressed in red, stood still while the other two were dressed in colours other than red but were   moving in the ring. The bull attacked the moving persons and left the motionless person wearing red clothing. (It means bull’s attack is not prompted by red colour).

              Conclusion is crystal clear; the bull is annoyed by the movement and not by red colour. Thanks to Discovery Channel which solved the sphinx riddle and helped us to reach the real cause of bull’s outrage.

              Still one question is irritating, if red colour is not irritating then why the muleta of red colour is used? The answer is: It is a concealing tactic; in the last stage of the bullfighting, when the bull meets its end, a dagger is run through in a way to hit bull’s heart and hence red colour rag helps to mask one of the horrible and terrifying aspects of bullfighting i.e. “the concealing of bull's blood”.