how do you conclude the focal length of lens depend upon the surrounding medium in which it is kept
Answers
we can conclude the focal length of lens depend upon the surrounding medium in which it is kept by performing simple experiment :
Material required :
Beaker, convex lens, measuring scale, water, circular lens holder, stone
Procedure :
By distant object method we can find the focal length of given lens [convex].
i) Take a beaker whose height is much greater than the focal length of the lens and fill it with water.
ii) Keep a black stone at the bottom of the vessel.
iii) Now dip the lens into water using circular lens holder such that it is at a distance which is less than or equal to focal length of the lens in air.
iv) Now see through the lens to have a view of the black stone.
v) Now increase the height of the lens till you are not able to see the stone’s image.
observation
When the lens is dipped to a height which is greater than the focal length of lens in air, we are able to see the image.
conclude :
By this experiment we can conclude that focal length of lens depends upon surrounding medium.
The focal length of a lens is depended on the surrounding medium. The reason behind this phenomenon is that the angle of refraction of a lens is depended on the indices of refraction of the medium of lens and the incoming medium and the difference in their indices.
We can find the lens’s dependency on its surrounding through a simple experiment. For conducting the experiment, one needs some equipment like glass beaker, convex lens, water, lens holder stone and measuring scale.
Fill some clear water in a glass beaker which has a height that is greater than the focal length of the lens. Now place a dark colored stone at the bottom of the beaker. Next step is to dip the circular lens into water with a lens holder. Try to focus the stone at the bottom of the beaker through the lens and keep raising the height of the lens until it become hard to see the stone through the lens.