Mirages

 

Mirages

        Mirage is an optical illusion where it appears that water has collected on the road at a distant place but when we get there, we don't find any water.

Do you know the reason why it appears  so?  

Let us see...

         

                             

            The formation of a mirage is the best example where refractive index of a medium varies throughout the medium.

            During a hot summer day, air just above the road surface is very hot and the air at higher altitudes is cool.It means that the temperature decreases with height. As a result density of air increases with height.We know that refractive index of air increases with density. Thus refractive index of air increases with height. So, the cooler air at the top has greater refractive index than hotter air just above the road. Light travels faster through thinner hot air than through the denser cool air above it.

                       

                                  

           

             When light from a tall object such as tree or from the sky passes through a medium above the road, whose refractive index decreases towards ground, it suffers, refraction and takes a curved path because of  total internal reflection.

            This refracted light reaches the observer in a direction. This appears to the observer as if the ray is reflected from the ground.

            Hence, we feel the  illusion of water being present on the road which is the virtual image of the sky and inverted image of tree on the road.

                      ***Thank You***