Prism Geometry and Deviation
For a prism in air, r1+r2=A and deviation delta=i+e-A, with all angles measured consistently from face normals.
Why this shows up in the exam
Prism ray tracing · Beam steering · Refractometer calculations
Learn the idea
A prism's total deviation is the sum of its two surface turnings. The ray bends at entry and again at exit, while the internal ray angles fit inside the prism angle.
🧠 Memory hook: Inside angles add to A; outside turns give delta.
Get this one clearly and it pays off every single time it shows up in the paper. 🎯
Formulas & facts to keep ready
- r1 + r2 = A — internal prism geometry
- delta = i + e - A — total angular deviation
How to approach it
- 1Draw normals at both faces
- 2Use Snell's law and r1+r2=A
- 3Compute delta=i+e-A
Common slip-ups that cost marks
- •Using face angles instead of normal angles
- •Writing i+e+A
- •Assuming a symmetric path for every incidence
🌟 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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