Where will be the image formed when an object is placed at focus of a concave lens

The characteristics of the image formed by a concave lens when an object is placed at infinity is/are:

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A tank is filled with water to a height of 12.5 cm. The apparent depth of a needle 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 up to the same height, by what distance would the mircoscope have to be moved to focus on the needle again?

Case I: When tank is filled with water. Given, real depth = 12.5 cm;           apparent depth = 9.4 cm Now, using the formula, 

                    μ = real depthapparent depth

Refractive index,  μ = 12.59.4 = 1.33

Case II: When water in the tank is replaced by another liquid.

apparent depth = real depthμ 

i.e., apparent depth = 12.51.63 = 7.67 cm

Distance through which microscope has to be moved downward is = (9.4 – 7.67) cm = 1.73 cm.