1. Images formed by lenses

2. Convex (converging) lenses, f>0.

3. Three light rays Parallel in, focus out; Focus in, parallel out; Centre in, centre out.

4. F f < d o <2 f FF f > d o F

5. Properties of the Image (convex lens) d o is the distance between the object and the lens f is the focal length. Distance to the mirrorProperties of the image d o >2 fInverted, diminished, real d o = 2 fInverted, same size, real f < d o <2 fInverted, magnified, real d o = fNo image d o < fupright, magnified, virtual

7. Images formed by a convex mirror The image is upright, diminished, and virtual, behind the mirror and between the mirror and the principal focus. F

8. Concave (diverging) lenses, f <0

9. Descartes’ formula f: focal length, negative when the lens is concave. d i : distance the image is in front of mirror, negative when image is virtual (behind lens). d o : distance the object is in front of lens.

10. Magnification h i : height of image, negative when image is virtual. h o : height of object.

11. eg1.An object 2cm high is placed 10cm in front of a concave lens of focal length 3.5cm. Find the height and position of the image.

12. Ans. d o = 10cm, h o =2cm, f=-3.5cm. d i =?, h i =? h i =-0.26h o =-0.26x2 = -0.52cm What does the negative sign stand for?