Answer :
Place a glass slab over a mark on a piece of paper and to refocus the microscope, you should move it 1 cm upward to adjust for the apparent shift due to the refractive index of the glass. So, the correct option is 1.
When a slab of glass with a refractive index of 1.5 is placed over a mark that a microscope is focused on, the microscope must be adjusted to account for the optical path length change caused by the glass slab.
The actual thickness of the glass slab is 3 cm, but due to refraction, the apparent thickness will be less. The apparent shift (s) in the position of the mark is given by the formula:
s = t(1 - 1/n),
where t is the actual thickness of the slab, and n is the refractive index of the glass. Plugging in the given values:
s = 3 cm (1 - 1/1.5),
s = 3 cm (1 - 2/3),
s = 3 cm (1/3),
s = 1 cm.
Therefore, to focus the microscope again on the mark, it should be moved 1 cm upward. The correct option is to move the microscope 1 cm upward. So, the correct option is 1.
