Images Formed by Lenses

12.2

Ray Diagrams for Lenses

• Ray diagrams can be used to predict characteristics of images using 3 rays, just like for concave & convex mirrors.

• Ray diagrams are simplified in 2 ways:– Partial reflection & refraction is ignored.– Refraction that occurs at each surface of the lens

is replaced by only one bend at the axis of symmetry.

Converging Lenses – Ray Diagram

Converging Lenses - Rules

• All rays that enter a converging lens parallel to the principal axis leave through the focal point.

• The centre of the lens acts like a flat piece of glass, so rays leave in the same direction that they entered.

• Any ray that enters a converging lens from the focal point leaves the lens parallel to the principal axis.

Diverging Lenses – Ray Diagram

Diverging Lenses - Rules

• All rays that enter a diverging lens parallel to the principal axis leave as though they were coming from the virtual focal point on the object side.

• The centre of the lens acts like a flat piece of glass, so rays leave in the same direction that they entered.

• Any ray that is directed toward the focal point on the opposite side of the diverging lens leaves the lens parallel to the principal axis.

Thin Lens Equation

Thin Lens Equation

• We will only be using the equations for calculations with converging lenses.