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
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
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
