Question

The image of point 'P' when viewed from top of the slab combination, will be formed at position.

• A. 1.5 cm above P
• B. 2 cm above P
• C. 1 cm above P
• D. 2 cm below P

Answer 1

The correct option is C 1 cm above P

Observer will see the image of 'P' when rays emanating from 'P' reaches the eye of observer.
For the given combination, net shift is only produced by two slabs with $\mu =1.5,$
$S_{net}=S_1+S_2$
$\Rightarrow S_{net}=t_1(1-\frac{1}{{\mu }_1})+t_2(1-\frac{1}{{\mu }_2})$
or, $S_{net}=1.5(1-\frac{2}{3})+1.5(1-\frac{1}{3})$
$\Rightarrow S_{net}=0.5+0.5=1cm$
Normal shift will be produced in direction of incident ray, thus image of 'P' will appear 1 cm above 'P'.

Why this question? Tip: Whenever an observer and object is given, first identify the direction of incident ray. Net shift is in direction of incident light from object.