Parallel Slab and Lateral Displacement
For a slab of thickness t with parallel faces, incidence angle i and refraction angle r, lateral shift is t sin(i-r)/cos r; this assumes the same external medium on both sides.
Why this shows up in the exam
Optical windows · Beam steering plates · Glass-slab refractive-index experiments
Learn the idea
A parallel-sided slab sends the emergent ray parallel to the incident ray but shifted sideways. The first face bends the ray and the second face undoes the angular change, not the sideways travel accumulated inside.
🧠 Memory hook: Parallel faces restore direction, not position.
Get this one clearly and it pays off every single time it shows up in the paper. 🎯
Formulas & facts to keep ready
- d = t sin(i-r)/cos(r) — lateral shift through a parallel slab
- e = i — parallel emergence when external media are identical
How to approach it
- 1Apply Snell's law at entry
- 2Use face parallelism at exit
- 3Resolve the internal geometry for lateral shift
Common slip-ups that cost marks
- •Calling the emergent ray undeviated in position
- •Using normal thickness along the ray
- •Assuming e = i with different outer media
🌟 That's the whole idea — you've got this. Try the practice set below; every question you attempt makes it stick a little harder.
Original chapter practice
Original questions for this chapter, not past-paper questions or an exact mapping to this individual concept.
A real object is placed 30 cm from a converging lens of focal length 10 cm. Find the real image distance.
More from Optics
Interference of light
Examine the principle of superposition, Young's double slit experiment, fringe width, intensity distribution, and the conditions for constructive and destructive interference.
Diffraction of light
Understand the bending of light around obstacles, single slit diffraction patterns, their width, and the effect of wavelength on diffraction.
Lenses and mirrors
Explore the image formation, ray diagrams, lens and mirror formulas, and the behavior of light with concave/convex lenses and mirrors, including combinations and virtual objects.
Optical instruments
Understand the working principles, magnification, resolving power, and design of devices like microscopes and telescopes, including their adjustments and measurement techniques.
Polarization of light
Learn about the polarization of light, Brewster's law, Malus' law, and the use and function of polaroids.
Dispersion and rainbow formation
Study how light splits into its constituent colors through dispersion in prisms and natural phenomena like rainbows, including minimum deviation and dispersive power.