
Let C be the critical angle.
Then, sinC=μ1, where, μ is the refractive index of glass.
So, sinC=21⇒C=45∘
As the angle of incidence is equal to the critical angle, so using Snell's law,
sinC=μsinθ
⇒21=2sinθ
⇒θ=30∘
Now, lateral displacement of the ray is
x=tsin(i−r)secr
⇒x=3sin(45∘−30∘)sec30∘
⇒x=3(0.26)(32)
⇒x=0.52cm
⇒x=52×10−2cm