Snell's Law at a Plane Interface
For isotropic media and angles measured from the normal, n1 sin(i) = n2 sin(r). The relation follows from phase matching at a stationary plane boundary.
Why this shows up in the exam
Underwater viewing · Window design · Ray tracing through transparent media
Learn the idea
Refraction changes a ray's direction so that refractive index times sine of angle is conserved across an interface. A ray bends toward the normal on entering the optically denser medium and away on entering the rarer medium.
🧠 Memory hook: Higher n pulls the ray closer to the normal.
Get this one clearly and it pays off every single time it shows up in the paper. 🎯
Formulas & facts to keep ready
- n1 sin(i) = n2 sin(r) — Snell's law for a plane interface
How to approach it
- 1Draw the normal
- 2Label incident and refracted media
- 3Apply n1 sin i = n2 sin r and check bending direction
Common slip-ups that cost marks
- •Measuring from the interface
- •Assuming denser means greater mass density
- •Using degrees and radians inconsistently
🌟 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.
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