Download Lens

Physics Lesson Plan
Teacher
Howard
Unit Title Refraction
Length
75
Goal(s)/PLO(s):
Course
Grade Level
Block/Period
identify any of the following from an appropriate
diagram: principal axis principal focus focal length
focal plane
identify a lens as converging (convex) or diverging
(concave)
Phys 11
11
C
Date
Class Size
Lesson #, of
Fri May 21
24
15-2
conduct an experiment to determine the focal length
of a convex lens
draw accurate scale diagrams for both convex and
concave lenses to show how an image is produced
describe the characteristics of images produced by
converging and diverging lenses
Materials:
Ray box, lenses, rulers, protractors, drinking straws, tape, model eye convex lenses
worksheet
Timeline
Class Activities
Introduction
Body
Notes 15-2 (omit combination of lenses)
Demo 4, 5 (OR QUICK LAB), 6
Closure
Notes 15.2 Lenses
When light refracts through a pane of glass the light is refracted
towards and away from the normal by the same amount. The
direction of the ray did not change, it is just offset.
If the surface is curved the alignment of the normal is different at
different points so the direction of the refracted ray changes from
point to point.
Lens
• Object with at least one curved surface that refracts light
• Demo 4 and 5 show concave and convex lens refracting light
o Do it from both sides to show that there are 2 focal
points but one focal length
o Draw 15-7
o geometric-optics_en.jar
Ray diagrams can be used to locate the image
Ray
Parallel
Central
Focal
Ray
Parallel
Central
Focal
From object to lens
Parallel to principal axis
To the centre of the lens
Passes through the focal point F
From object to lens
Parallel to principal axis
To the centre of the lens
Toward back focal point F
From converging (vex) lens to image
Passes through focal point F
From the centre of the lens
Parallel to the principal axis
From diverging (cave) lens to image
Directed away from focal point F
From the centre of the lens
Parallel to the principal axis
There are six possible types of images for a converging lens
depending on the location of the object (sketch figure 15-3 with the
descriptions)
1. object at infinity, image at F (burning ants)
2. Object outside 2F, real, small image between F and 2F.
(camera or eye lens)
3. Object at 2F, real image at 2F same size as the object
(inverting telescope)
4. Object between F and 2F, real, magnified image outside 2F
(movie projector)
5. Object at F, image at infinity (searchlights)
6. Object inside F, magnified virtual image on same side of
the lens as the object (telescope or magnifying glass)
Diverging lenses only produce virtual images (draw 15-9)
The magnification equation still applies (image/object)
People who’s eyes do not focus properly can be helped by wearing
glasses or contact lenses
• Demo with model eye
Farsighted (see far things well)
• Hyperopia
• Eye is too short
• Corrected with a converging lens
Nearsighted (see near things well)
• Myopia
• Eye is too long
• Corrected with a diverging lens
Assign worksheet