A) behave as a perfect reflector
B) absorb all light falling on it
C) have refractive index one
D) have refractive index exactly matching with that of the surrounding fluid
Correct Answer: D
Solution :
From the formula for refraction through a lens, focal length (f) is \[\frac{1}{f}=(n-1)\left( \frac{1}{R}-\frac{1}{{{R}_{2}}} \right)=0\] where n is refractive index of the material of the lens and \[{{R}_{1}},{{R}_{2}}\] are the radii of curvature of its surfaces. If the lens is immersed in a liquid whose refractive index is equal to the refractive index of the material of the lens \[{{(}_{a}}{{n}_{l}}{{=}_{a}}{{n}_{g}}),\]then \[_{l}{{n}_{g}}=\frac{_{a}{{n}_{g}}}{_{a}{{n}_{l}}}=1\] \[\therefore \] \[\frac{1}{f}=(1-1)\left( \frac{1}{R}-\frac{1}{{{R}_{2}}} \right)=0\] That is focal length of lens becomes infinite. Now the lens will behave just like a plane transparent plate and will become invisible. Alternative: When the refractive index of two mediums are exactly same, then there will not occur refraction and reflection at the common surface of separation due to which the visibility is observed.
You need to login to perform this action.
You will be redirected in
3 sec
