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$\frac{d-b}{a+b-c-d}$
