1. Optics 1
And you

2. Simplify the lens Upper and lower prism, with a cube in the middle.
Light rays enter the prisms and are refracted. And rays straight through the cube as well.
This area of intersection is known as the focal point (f)

3. A thick lens will have a shorter focal point
As well as a shift (offset) in the rays moving through the cube at an angle
focal length
Note the rays enter and leave the cube at the same angle –
but offset by this much

4. So we will always assume
We are dealing with a thin lenses with little offset distortion

5. Lens demo here!!!

6. Lens Diagram do = 2f Draw:
A lens with an x axis going through it
A point in the middle of the lens, at 3cm and 6 cm on either side (on x axis)
Label as follows: note: do and di are 2x focal length
A line 1.5 cm up at do
A line 1.5 cm down at di
Label ho (object) and hi (image)
Ray 1 parallel to x axis, ray 2 through f, and ray 3 through the center lens.
ho = 1.5cm high
Focus = 3cm
di = 6cm
focus = 3cm
do = 6cm hi

7. The fun math part
hi / ho = (di – f) / f (di – f) / f = di / do di / do = hi / ho Lens equation: 1/do + 1/di = 1/f f
di = 6cm ho
focus = 3cm
do = 6cm hi

8. The Signs f is + with converging lens
do is when obj. and light are on same side of lens (almost always)
di is when image on opp. Side of lens from object
ho is always (so hi is negative here)
M (magnification) = hi / ho = -di /do
ho = 1.5cm high
Focus = 3cm
di = 6cm
focus = 3cm
do = 6cm hi

9. Second lens diagram do = 1.5f
f = 3 cm , ho = 1.5 cm
When you are finished, measure di
Then use the lens equation to calculate what di should be
di = 9 cm

10. Did your diagram look like this?

11. Now please diagram do = f
f = 3 cm, ho = 1.5 cm

12. Did yours look like this??
No intersection = no image!!!!!!!!!!!!!!

13. Now diagram do = .8f make this one large – start in the middle of the page
f = 3 cm, ho = 1 cm

14. Notice intersection is on object side of lens = magnification

15. ? di in this situation? Lens equation: 1/do + 1/di = 1/f
* note di will be negative here (not on opposite side of lens
di = - 12 cm

16. Convex and concave
Converging diverging
spoon, car mirror f f