Question

If two glass slabs are attached, what will be the direction of refracted ray and emergent ray?

Answer 1

(Snell's Law) the index of refraction (ior) of a transparent material expresses how much it bends light. It's 1.0 if it doesn't bend at all. So the ior of empty space is 1.0. Air's iof is something like 1.001. The highest it gets is around 2. Some exotic glasses/plastics are 2.5 or more. (Lead doesn't have a "really high" ior. It doesn't have an ior at all, because it's not transparent.)

Let's say the 2 types of glass are g1 & g2. Say a light ray goes from g1 into g2, whose iof's are, res, i1 & i2. The angle of the in/out rays are, res, A1/A2, the angles between the ray and the "normal" (direction perpendicular to the 2 surfaces.)

Snell's Law:

sin(A1) / sin(A2) = i2 / i1.

So if the 2 slabs are made of the same glass, then i1 = i2, So i2/i1 = 1, so sin(A1) = sin(A2), so A1 = A2, meaning there's no change in the ray's angle. A higher ior causes a smaller angle. That's why the 1's and 2's are reversed in the formula.

Answer 2

If both pieces of glass have the same refractive index and have parallel surfaces, the rays in and out will be parallel.