Lesson 11 of 13
The big picture
Show on a big screenKeep this table beside your book.
| Topic | The key line |
|---|---|
| Reflection | i = r, both from the normal, in one plane. |
| Curved mirror | f = R/2. F is halfway from P to C. |
| Image by a concave mirror | Between C and F: real, inverted, bigger. Inside F: virtual, upright, bigger. |
| Image by a convex mirror | Virtual, upright, smaller, for a real object anywhere. |
| Ray diagram | Any two standard rays cross, or seem to cross, at the image. |
| Mirror formula | 1/v + 1/u = 1/f, m = −v/u |
| Refraction | Into a higher n: towards the normal. Into a lower n: away. sin i / sin r is fixed. |
| Lens formula | 1/v − 1/u = 1/f, m = v/u |
| Image by a concave lens | Virtual, upright, smaller, for a real object anywhere. |
| Power | P = 1/f, f in metres. Unit: dioptre. |
| Glass slab | A ray in air leaves parallel to the ray that entered, shifted sideways. The gap between the rays is the lateral displacement. |
The scooter's bulb sits at the focus of its concave mirror. Rays that leave the focus come out parallel. That makes a long beam.
Read Chapter 9, Light – Reflection and Refraction, in your book. Try its exercises. The Human Eye and the Colourful World comes next.