Laws of Reflection and Ray Geometry
At a smooth reflecting surface, incident ray, reflected ray and normal are coplanar, and the angles measured from the normal are equal.
Why this shows up in the exam
Periscopes · Solar concentrator alignment · Ray tracing in cameras
Learn the idea
A reflected ray leaves a surface at the same angle to the normal as the incident ray. The normal acts like the hinge line of a bounce: the incident and reflected directions are symmetric about it.
🧠 Memory hook: Reflect about the normal, not about the surface.
Get this one clearly and it pays off every single time it shows up in the paper. 🎯
Formulas & facts to keep ready
- i = r — angles of incidence and reflection, both measured from the normal
How to approach it
- 1Draw the normal
- 2Mark the incident angle from the normal
- 3Reflect the direction symmetrically
Common slip-ups that cost marks
- •Measuring angles from the mirror
- •Putting rays in different planes
- •Treating a shadow boundary as a reflected ray
🌟 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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