Mirages in deserts are observed. Give reason..
Answers
For exhausted travelers in the desert, an inferior mirage may appear to be a lake of water in the distance. An inferior mirage is called "inferior" because the mirage is located under the real object. The real object in an inferior mirage is the (blue) sky or any distant (therefore bluish) object in that same direction. The mirage causes the observer to see a bright and bluish patch on the ground in the distance.
Light rays coming from a particular distant object all travel through nearly the same air layers and all are bent over about the same amount. Therefore, rays coming from the top of the object will arrive lower than those from the bottom. The image usually is upside down, enhancing the illusion that the sky image seen in the distance is really a water or oil puddle acting as a mirror.
Rajdeep here....
What is a mirage?
A mirage is an optical illusion, usually observed in deserts or places with hot conditions. Now, your question is, "Why do we observe mirage?"
Answer:
Actually, the lower layers of atmosphere are denser than the upper layers. However, in deserts, during day, the sand absorbs too much heat and becomes hot, due to which the lower layers (near the ground) become rarer than the upper. We know, when light ray (from a tree) enters a rarer medium (lower layer) from a denser medium (upper layer), the ray bends away from the normal.
So, as light rays from a tree enter the successive lower rarer layers from the upper denser layers, the light continuously bends away from the normal after each successive stage of refraction. At a certain stage, the light suffers Total Internal Reflection, and the light ray reflects from the lowermost layer (you can say, from a point just above the hot ground) and reaches the eye of the observer. Human eyes can follow a straight path. When the ray reaching the eye is extended backwards, an inverted image of the tree is seen on the ground, as you see an image of the tree in water in a pond. Thus the observer is befooled as he concludes that there is water. However, actually there is no water!!
Hope my answer is satisfactory...
Thanks!!