Question

How much time will light take to cross 2mm thick glass pane if refractive index of glasses is 3/2?

Answer 1

time d/s
speed= 3 lakh/3/2=4.5 lakh
distance=2mm=.002m
time=.002/4.5 lakh
=..........

Answer 2

The thickness of the glass pane [t] = 2 mm.

        $1\ mm=10^-3\ m$

        $Hence\ t=2*10^-3\ m$

The refractive index of the glass is 3/2 i.e 1.5.

The refractive index of the glass is defined as -

                                             $\mu =\frac{c}{v}$

Here c is the velocity of light in air.

        v is the velocity of light in glass pane.

$\mu\ is\ the\ refractive\ index\ of\ the\ glass$

The velocity of light in glass pane [v]  $=\frac{c}{\mu}$

                                                               $=\frac{3*10^8\ m/s}{1.5}$

                                                               $=2*10^8\ m/s$

The time taken by light to cross the glass pane-

                                               $T=\frac{t}{v}$

                                                $=\frac{2*10^-3\ m}{2*10^8\ m/s}$

                                                 $=\ 10^-11\ s$    [ans]