Question

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

• A. $0.4$
• B. $1.8$
• C. $1.2$
• D. $1.6$

Answer 1

The correct option is C $1.2$

The normal swift (N) for the glass slab is derived by :-

$n=Ad=t(1-\frac{1}{u})$ Where $\Delta d:$ Distance between object t image $t_1$ thickness of slab.

From figure, $\Delta d=2cm$.

$\Rightarrow 2=6(1-\frac{1}{u})\Rightarrow 1-\frac{1}{u}=\frac{1}{3}$

$\Rightarrow u=\frac{3}{2}$