Lenses can bend light to make images appear larger or smaller, upright or inverted. A lens is a transparent piece of glass or plastic with one or more curved sides. Converging lenses bring parallel rays of light together and produce real, inverted images beyond the focal point. Diverging lenses spread parallel rays of light and always form smaller, upright, virtual images on the same side as the object. Lenses have a focal point on each side and obey three rules for how rays of light pass through based on their angle of incidence.

1. LENSES

2. Lenses can change the appearance of objects, making images appear
larger or smaller than the object or making them upside down or even
misshapen because of refraction.
LENSES

3. A lens is a thin, transparent piece of glass or plastic that has at least
one curved side. The curved side or sides may be concave or convex.
A Converging Lens A Diverging Lens
makes parallel light rays come
together
makes parallel light rays move apart
LENSES

4. principal Focus
secondary principal Focus
Since lenses have 2 sides, they have a focal point on each side.
The secondary principal focus is on the same side of the lens as the
incident rays
CONVERGING LENSES

5. There is also 2F and 2F’. These two points are twice the distance away
from the optical centre than the focus points.
FF’ 2F2F’
CONVERGING LENSES

6. 3 TYPES OF RAYS
1) Any ray that enters a lens parallel to the principal
axis will pass through the focal point on the other side
of the lens.
2) Any ray that travels through the centre of the lens
will keep travelling in the same direction.
3) Any ray that enters the lens from the focal point
will leave the lens parallel to the principal axis.
CONVERGING LENSES

7. 1) Any ray that enters a lens parallel to the principal axis will
pass through the focal point on the other side of the lens.
FF’
CONVERGING LENSES

8. 2) Any ray that travels through the centre of the lens will keep
travelling in the same direction.
FF’
CONVERGING LENSES

9. 3) Any ray that enters the lens from the focal point will leave
the lens parallel to the principal axis.
FF’
CONVERGING LENSES

10. Draw the ray diagram for this pencil to locate its image (you
need 2 rays)
,
2F2F
,
CONVERGING LENSES

11. Draw the ray diagram for this pencil
(you need 2 rays)
,
2F
2F
,
CONVERGING LENSES

12. Draw the ray diagram for this pencil
(you need 2 rays)
,
2F
2F
,
CONVERGING LENSES

13. Draw the ray diagram for this pencil
(you need 2 rays)
,
2F
2F
,
CONVERGING LENSES

14. S- SAME SIZE
A- Inverted
L- At 2 F
T -Real
,
2F
2F
,
If the object is at 2F’…
CONVERGING LENSES

15. The first lens known to be used was a converging lens called a reading
stone. Reading stones formed images that were upright and larger
than the object.
How can a converging
lens produce both
upright and inverted
images?
CONVERGING LENSES

16. Draw the ray diagram for this pencil to locate its image (you
need 2 rays)
,
2F2F
,
CONVERGING LENSES

17. ,
2F2F
,
Draw the ray diagram for this pencil to locate its image (you
need 2 rays)
CONVERGING LENSES

18. ,
2F2F
,
Draw the ray diagram for this pencil to locate its image (you
need 2 rays)
CONVERGING LENSES

19. ,
2F2F
,
Draw the ray diagram for this pencil to locate its image (you
need 2 rays)
CONVERGING LENSES

20. ,
2F2F
,
S- Larger
A- Upright
L- Behind the lense
T- Virtual
If the object is between F’ and the lens…
CONVERGING LENSES

21. DIVERGING LENSES

22. Since lenses have 2 sides, they have a focal point on each side.
The secondary principal focus is on the same side of the lens as the
incident rays
DIVERGING LENSES

23. DIVERGING LENSES

24. F’F 2F’2F
The same focal points as those for converging lenses, except the principal
focus is on the same side as where the incident rays are coming from
O
Optical centre
DIVERGING LENSES

25. 3 TYPES OF RAYS
1) Any ray parallel to the principal axis is refracted as
if it had come through the principal focus (F)
2) A ray that appears to pass through the secondary
principal focus (F’) is refracted parallel to the principal
axis
3) A ray through the optical centre (O) continues
straight through its path
DIVERGING LENSES

26. F’F 2F’2F O
1) Any ray parallel to the principal axis is refracted as if it had
come through the principal focus (F)
DIVERGING LENSES

27. F’F 2F’2F O
2) A ray that appears to pass through the secondary principal
focus (F’) is refracted parallel to the principal axis
DIVERGING LENSES

28. F’F 2F’2F O
3) A ray through the optical centre (O) continues straight
through its path
DIVERGING LENSES

29. F’F 2F’2F O
Draw the ray diagram for this pencil to locate its image (you
need 2 rays)
DIVERGING LENSES

30. F’F 2F’2F O
Draw the ray diagram for this pencil to locate its image (you
need 2 rays)
DIVERGING LENSES

31. F’F 2F’2F O
Draw the ray diagram for this pencil to locate its image (you
need 2 rays)
DIVERGING LENSES

32. F’F 2F’2F O
Draw the ray diagram for this pencil to locate its image (you
need 2 rays)
DIVERGING LENSES

33. F’F 2F’2F O
S- Smaller
A- Upright
L- On the same side of the lens as the object
T- Virtual
For ALL images from diverging lenses…
DIVERGING LENSES