# Two rays of light are incident normally on a tub of height #H# filled with water. They pass through glass slabs of heights #h_1# and #h_2#. If the speed of light in vacuum is #c#, what is the time difference between the rays of light to reach the bottom?

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Refractive indices of water and glass are #4/3# and #3/2# respectively.

Refractive indices of water and glass are

##### 1 Answer

The situation described in the problem is shown in the above figure

As the rays of light are incident normally , the rays will refracted through the media without deviation.

**For slab of height**

the total path length of water and glass =H

Path length of glass medium

Then path length of water medium

**For slab of height**

the total path length of water and glass =H

Path length of glass medium

Then path length of water medium

We know refractive index of water

Again we know refractive index of glass

**Calculation of time to reach #color(red)(ray_1) # at the bottom from surface**

So time taken by the light

And time taken by the light

Hence **total time**

**Calculation of time to reach #color(red)(ray_2) # at the bottom from surface**

Now time taken by the light

And time taken by the light

Hence **total time**

Hence the time difference between the two rays of light to reach the bottom is given by