The overhead projector is 2.0 m from the screen. I place a slide on the deck over the
overhead to project it. I need to make the image larger, so I must move the overhead
back from the screen.
This makes the image out of focus. How do I need to move the lens in order to restore
1 +1 = 1
s s' f
Lower it toward the slide
Doing the Numbers
A student looks at a 2.0 cm high object through a diverging lens of focal length -10 cm.
The object is 20 cm from the lens.
Where does the image appear to be? How large is it?
1 1 −1
20 s' = 10
1 −1 1
s'= 10 − 20
s’ = -6.7 cm
Image is upright
The Diverging Mirror
A ray that enters parallel to the optical axis appears to have come from the focal point
A ray that enters heading for the focal point emerges parallel to the optical axis
Images are small
Large field of view