A tank is filled with water to a heigth of 12.5 cm. The apparent depth of a needle lying at the bottom of the tank is measured by a microscope t be 9.4 cm. what is the refractive index of water ? If water is replaced by a liquid of refractive index 1.63 upto the same hight, by distance would the microscope have to be moved to focus on the needle again?

Explanation

` n_(wa) = ("Real depth")/("Apparent depth") = (12.5)/(9.4) = 1.33 " " n_("is") = (12.5)/(d_(l)) = 1.63`
`therefore d_(l) = (12.5)/(1.63) = 7.66` cm
i.e., depth in liquid = 7.66 cm
Distance through which microscope has to be moved = 9.4 - 7.66 = 1.74` cm