question_answer

A ray of light passes through a glass plate of thickness t and refractive index u. 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,   \[time=\frac{\text{distance}}{velocity\,in\,glass}\] ?..(ii) From Eqs. (i) and (ii), we get \[time=\frac{t\mu }{c}\]