rules for concave/convex refractions + key terms for ray diagrams

how do lenses form images

by refracting light

a axis is

a line passing through middle of lens - - - -

a convex lens causes aka converging lens

rays of light parallel to axis to converge

a concave lens causes aka diverging lens

rays of light parallel to axis to diverge meaning spread out

convex principle focus is

where rays hitting lens parallel to axis all meet

concave principle focus is

when rays of light hitting axis appear to all meet

focal length is

distance from centre of lens to principle focus (which is on either side)

3 rules for convex lens refraction

a incident ray parallel to axis refracts through lens and passes through principle focus on other side

a incident ray passing through principle focus refracts through lens and travels parallel to axis

a incident ray travelling through centre of lens carries on in same direction

concave lens refraction rules

a incident ray travelling parallel to axis will refract in lens and travel in line with principle focus

a incident ray travelling towards principle focus refracts in lens and travels parallel to axis

a incident ray passing through centre of lens carries on in same direction