1. Lenses
and
Ray Diagrams

2. A shaped piece of glass or other transparent material is capable of taking parallel rays of incident light and either

3. converging them to a point…
converging lens

4. or diverge them from a point.
Such a piece of glass is referred to as a lens.
diverging lens

5. Converging lens parallel rays of light converge.
identified by their shape; they are thicker across their middle and thinner at their upper and lower edges.
Diverging lens
parallel rays of light diverge.
identified by their shape; they are thinner across their middle and thicker at their upper and lower edges.

6. Converging lens

7. Thin lens ray diagrams
To simplify ray diagram construction the refractions at the two surfaces are not shown. Refraction occurs at the centre line of the lens.
RAY 1
Converging lens F F

8. Converging lens
RAY 2 F F

9. Converging lens
RAY 3 F F

10. Converging lens F F

11. Diverging lens
RAY 1 F F

12. Diverging lens
RAY 2 F F

13. Diverging lens F F

16. A diverging lens always produces an image that is virtual, erect and smaller than the object.

17. Refraction Rules for a Converging Lens
Any incident ray travelling parallel to the principal axis of a converging lens will refract through the lens and travel through the focal point on the opposite side of the lens.
Any incident ray travelling through the focal point on the way to the lens will refract through the lens and travel parallel to the principal axis.
An incident ray which passes through the center of the lens will in effect continue in the same direction that it had when it entered the lens.

18. Refraction Rules for a Diverging Lens
Any incident ray travelling parallel to the principal axis of a diverging lens will refract through the lens and travel in line with the focal point (i.e., in a direction such that its extension will pass through the focal point).
Any incident ray travelling towards the focal point on the way to the lens will refract through the lens and travel parallel to the principal axis.
An incident ray which passes through the center of the lens will in effect continue in the same direction that it had when it entered the lens.

19. Diverging lens
RAY 3 F F