question_answer

A ray of light passes through a glass plate of thickness t and refractive index n. If the speed of light in vacuum is c, then the time taken by light in passing through the plate will be :

A)  \[\mu t\]                                           

B) \[\frac{\mu t}{c}\]

C)  \[\frac{tc}{\mu }\]                                         

D)  \[\frac{t}{\mu c}\]

Correct Answer: B

Solution :

                 Refractive index\[(\mu )\]is defined as \[\mu =\frac{{{v}_{0}}}{{{v}_{g}}}\]                               ...(i) where\[{{v}_{0}}\]is velocity in vacuum and\[{{v}_{g}}\]in glass. Also,  \[time=\frac{distance}{velocity\text{ }in\text{ }glass}\]         ... (ii) From Eqs. (i) and (ii), we get \[time=\frac{t\mu }{c}\]