A tank is filled with water to height of 12.5 cm. The apparent depth of a needl lying at the bottom of the tank is measured by a microscope to 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 height, by what distance would the microscope have to be moved to focus on the needle again?

Explanation

Here real depth =12.5 cm , apparent depth =9.4 cm `, mu = ? `
`:. , mu = (12.5 ) /( 9.4) = 13.3`
Now in the second case `mu = 1.63 `
real depth =12.5 cm , apparent depth `d_(ap) = ? `
` :. , 1.63 = (12.5)/(d _(ap))`
`rArr d_(ap) = (12.5)/( 1.63) = 7.67 cm`