One face of a rectangular glass plate 6 cm thick is silvered. An object held 8 cm in front of the first face forms an image 12 cm behind the silvered face. The refractive index of the glass is

One face of a rectangular glass plate 6 cm thick is silvered. An object held 8 cm in front of the first face forms an image 12 cm behind the silvered face. The refractive index of the glass is

A) 0.4     B) 0.8    C) 1.2     D) 1.6

Concepts: Refractive index cannot be less than 1. So the first two choices can be eliminated at the first sight. AD-Apparent Depth, AS-Apparent Shift.

In plane mirror,

\[object\hspace{2mm}distance=image\hspace{2mm}distance\]

Now the mirror is shifted to a new position. so,

\[8\hspace{2mm}cm+AD=AS+12\hspace{2mm}cm\]

\[8\hspace{2mm}cm+\frac{6}{n}=\left(6-\frac{6}{n}\right)+12\hspace{2mm}cm\]

\[n=1.2 \]