question_answer

A beam of light is converging towards a point \[I\] on a screen. A plane glass plate whose thickness in the direction of the beam = \[t\], refractive index = \[\mu \], is introduced in the path of the beam. The convergence point is shifted by [MNR 1987]

A)            \[t\,\left( 1-\frac{1}{\mu } \right)\] away                    

B)            \[t\,\left( 1+\frac{1}{\mu } \right)\] away

C)            \[t\,\left( 1-\frac{1}{\mu } \right)\] nearer                 

D)            \[t\,\left( 1+\frac{1}{\mu } \right)\] nearer

Correct Answer: A

Solution :

                   Normal                    shift \[\Delta x=\left( 1-\frac{1}{\mu } \right)\ t\]           and shift takes place in direction of ray.