Q29. A light ray is incident on a glass slab of thickness $4 \sqrt { 3 } \mathrm {~cm}$ and refractive index $\sqrt { 2 }$. The angle of incidence is equal to the critical angle for the glass slab with air. The lateral displacement of ray after passing through glass slab is $\_\_\_\_$ $\mathrm { cm } . \left( \right.$ Given $\left. \sin 15 ^ { \circ } = 0.25 \right)$