question_answer

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                                 [CPMT 1999]

A)            0.4

B)            0.8

C)            1.2 

D)            1.6

Correct Answer: C

Solution :

                   Let x be the apparent position of the silvered surface.                    According to property of plane mirror                    x + 8 = 12 + 6 ? x  \[\Rightarrow \]x = 5 cm            Also\[\mu =\frac{t}{x}\]\[\Rightarrow \]\[\mu =\frac{6}{5}=1.2\]