Ray Diagrams
Convex Lens
Ray Diagrams Lenses
To draw ray diagrams for lenses use two of the
following rays:
1. From the tip of the object horizontally toward
the lens, refracting through the focal point . .
. extend the virtual ray behind (on the left
side) of the lens.
2. From the tip of the object straight through the
center of the lens . . . extend the virtual ray
behind the lens.
3. From the tip of the object through the opposite
f, refracting horizontally . . . extend the
virtual ray behind the lens.
Can make any kind of image:
Convex Lens:
Converge light
Have (+) focal points
magnified or minimized
upright or inverted
virtual or real
-2f
-f
+f
+2f
minimized
inverted
real
-2f
-f
+f
+2f
EQUATIONS
1 / Di + 1 / Do = 1 / f
- (Di) / Do = Hi / Ho = m
 Di = distance from the lens or mirror to the image
 Do = distance from the lens or mirror to the object (always
POSITIVE)
 f = distance from the lens or mirror to the focal point (focal
length) be sure to plug in the correct sign!!!!!!
 m = magnification
 Hi = height of image
 Ho = height of object
EQUATIONS
If you get:
+ Di then the image is REAL
- Di then the image is VIRTUAL
+ Hi then the image is UPRIGHT
- Hi then the image is INVERTED
the absolute value of Hi < Ho then the image is MINIMIZED
the absolute value of Hi > Ho then the image is MAGNIFIED
the absolute value of Hi = Ho then the image is the SAME size.
SAMPLE PROBLEM
If a converging lens has a focal length of 6 cm ,
describe the image formed of a 2 cm tall flower that is
3 cm from the lens.
Di = ?
Do = 12 cm
f = 6 cm
1 / Di + 1 / Do = 1 / f
1 / Di + 1 / 3 = 1 / 6
Di = - 6 cm. . . . .the image is VIRTUAL
(because Di is negative)
SAMPLE PROBLEM, cont.
Hi = ?
Ho = 2 cm
Di = - 6 cm
Do = 3 cm
-(Di) / Do = Hi / Ho
-(-6) / 3 = Hi / 2
Hi = 4 cm. . .the image is UPRIGHT (because Hi is
positive) and maximized (because Hi > Ho)