Transcript Ray Diagrams: Concave Mirrors

Lens Ray Diagrams
2 types of lenses just like mirrors
Convex Lens - Converging - thick in
middle, thin edge - Opposite of mirror
Concave Lens - Diverging - thin in
middle, thick edge
General Information for all
lenses
• The principle axis still exists line parallel to
center of lens
• The focal point is no longer 1/2 distance from
CC
• The focal point depends on both curvature
and the way the lens refracts light
• There are 2 focal points. f1 and f2- one on
each side of lens
• The ray method for lenses is similar to
mirrors.
Ray Diagrams: Convex Lens
• Ray #1: Light travels parallel & refracts
through focal point f2
• Ray #2: Light travels straight through the
center of the lens
• Ray #3: Light travels through first focal
point(f1) & refracts parallel to the principle
axis
•
Object at infinity - image located
at f2. This is one way to find the
focal point
1
1
2
2
Object located beyond 2f1 - image is located between f2 and 2f2
…Image real, inverted, smaller
1
1
2
2
Sample problem
A 3 cm object is located 12 cm from a
convex lens with a focal length of 3 cm.
Where would the image be located?
What is the size of the image?
Image Location
Given: So=3 cm do=12 cm f=3 cm
1/di + 1/do = 1/f
1/di = (1/f)-(1/do)
1/di = (1/3) - (1/12)
1/di = 4/12 - 1/12 = 3/12
di = 12/3 = 4 cm
What is the size of the image?
si/so = -di/do
si = -so di /do
- 4cm (3cm) /12 cm = -1 cm
Object located @ 2f1 - image is located at 2f2
…Image real, inverted, same size
1
1
2
2
Object located between 2f1 & f1 - image is beyond 2f2
… Image real, larger, inverted
1
1
2
2
Object located at f1
Rays refracted parallel - No Image
1
1
2
2
Object located closer than f1
… Trace diverging rays backwards
Image is erect, larger and virtual
1
1
2
2
Ray Diagrams: Concave
(Diverging) Lens
1st Ray: Parallel to the Principle axis, as
if it had come from the 1st focal point
(f1)
2nd Ray: Straight through the center of
the lens
3rd Ray: Heads toward 2nd focal point
(f2) & refracts parallel
Object at infinity - image located
at f1 and is virtual
1
1
2
2
Object located @ 2f1
……Image is virtual, upright, smaller
1
1
2
2
Object located between 2f1 and f1
……Image is virtual, upright, smaller
1
1
2
2
Object located @ f1
……Image is virtual, upright, smaller
1
1
2
2
Concave (Diverging) Lens
• Always form images that are
Virtual
Upright
Smaller