Drawing Concave and Convex Lenses
Section 11.3.a
Pgs. 450-454
Types of Lenses
A lens is a curved transparent material that is smooth and regularly shaped so that when light strikes it, the light refracts in a predictable and useful way.
Most lenses are made of glass or very hard plastic.
Lens Terminology
The axis of symmetry is an imaginary vertical line drawn through the optical centre of a lens.
The principal axis is an imaginary line drawn horizontally through the optical centre perpendicular to both surfaces.
The focal point where the light come to a focus is given the symbol F, while the opposite side is represented by F’.
F
F’
F
F’
Concave Lens
Convex Lens
The focal length, f, is the distance from the axis of symmetry to the principal focus measured along the principal axis.
F
F’
F
F’
Concave Lens
Convex Lens
f
f
f
f
Concave/Diverging Lenses
A concave lens is thinner in the centre than at the edges.
As parallel light rays pass through, they are refracted away from the axis of symmetry.
The light rays diverge and will never meet on the other side of the lens.
The image formed is always upright and smaller than the object.
Drawing Concave Lens Ray Diagrams
Step 1:
The first ray of a concave lens ray diagram travels from the tip of the object parallel to the principal axis.
When it emerges from the lens, it appears to come from the principal focus.
F
Step 2:
The second ray travels from the tip of the object through the optical centre of the lens, and is not refracted.
F
Step 3:
Draw the virtual image where the rays appear to intersect.
F
Convex/Converging Lenses
A convex lens is thicker at the centre than at the edges.
As parallel light rays travel through, they are refracted toward the axis of symmetry of the lens.
The rays move toward each other.
The light rays cross at the focal point of the lens.
Drawing Convex Lens Ray Diagrams
Step 1:
The first ray of a convex lens ray diagram travels from the tip of the object parallel to the principal axis.
When it emerges from the lens it passes through the principal focus.
F
Step 2:
The second ray travels from the tip of the object through the optical centre of the lens and is not refracted.
F
Step 3:
Draw the real image where the rays appear to intersect.
F
Seatwork / Homework
Read Section 11.3 (p. 448 – 454)
Learning Checkpoint # 1 – 4 (p. 454)
Copy Table 11.6 on pg. 451
Copy Table 11.7 on pg. 453