Write an activity to show that the focal length of a lens depends on its surrounding medium?
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.
HOPE U UNDERSTOOD
Explanation:
Take the same lens that was used in lab activity. Note the average focal length of the lens that was calculated in the activity. Take cylindrical vessel such as glass tumbler. Its height must be much greater than the focal length of the lens. (We require the vessel which has a length (depth) nearly equal to four times of the focal length of lens). Keep a black stone inside the vessel at its bottom Now pour water into the vessel up to a height such that the height of the water level from the top of the stone is greater than focal length of lens. Now dip the lens horizontally using a circular lens holder as shown in the fig.- (21) above the stone. Set the distance between
stone and lens that is equal to or less than focal length of lens measured in activity 2. Now look at the stone through the lens.