question_answer

A mark is made on the bottom of a beaker when it is empty and a microscope is focused on the mark. The microscope is then raised through 3 cm. To what height must water be poured in the beaker in order to bring the mark again in focus? (refractive index of water is 4/3)

A)  4.0 cm

B)  4.3 cm

C)  9.0 cm

D)  12.0 cm