Please see my attachment
They are asking the find the deviation d?
I know by snell's law n = sin i/sin r
where n is refractive index, i is angle of incidence and r angle of refraction.
so sin r = sin i/1.5 which gives 15 minutes(roughly) as the angle of refraction. but i dont know how to calculate d in cms. Please help, revered members

 

Please see my attachment
They are asking the find the deviation d?
I know by snell's law n = sin i/sin r
where n is refractive index, i is angle of incidence and r angle of refraction.
so sin r = sin i/1.5 which gives 15 minutes(roughly) as the angle of refraction. but i dont know how to calculate d in cms. Please help, revered members

Start by drawing triangles. Let one of the triagles have the side of length 1.95 cm in it, and let another triangle have the side of legnth d in it. You should be able to quickly and easiliy identify the angles for all triangles. Remember that if you know all the angles in a triangle and if you know the length of one side, you can find the length of the other 2 sides. I was able to quickly get the answer using 3 triangles. One triangle has a side with the length of 1.95, another has a side with the length of d, and the third triangle shares sides with the other 2 triangles, and allows the length of d to be related to the length of 1.95 cm.

In other words, it's just simple geometry, and the patience to work it out step by step.

EDIT: Note that you can do it by making 2 triangle also.