MCQ
A beaker containing liquid is placed on a table, underneath a microscope which can be moved along a vertical scale. The microscope is focussed, through the liquid onto a mark on the table when the reading on the scale is $a$. It is next focussed on the upper surface of the liquid and the reading is $b.$ More liquid is added and the observations are repeated, the corresponding readings are $c$ and $d.$ The refractive index of the liquid is
- ✓$\frac{{d - b}}{{d - c - b + a}}$
- B$\frac{{b - d}}{{d - c - b + a}}$
- C$\frac{{d - c - b + a}}{{d - b}}$
- D$\frac{{d - b}}{{a + b - c - d}}$
