Convex and concave lenses

1
Convex and concave lenses
convex lens
concave lens
2
Refraction by a convex lens
3
Focal length of a convex lens
4
Long short focal length
5
Focal length of a concave lens
6
Formation of a real image
7
Formation of a virtual image
8
Drawing ray diagrams real image
Important! All rays should have arrowheads on
them, showing direction of travel (Mine havent
because I ran out of time - sorry!)
Lens
Object
Optical Centre
Principal axis
F
Principal Focus
NOTE that the lens is drawn as a straight line
with arrowheads to represent its shape. This is a
convex lens.
9
Drawing ray diagrams some important notes

• Learn what the terms virtual, real, enlarged,
  diminished, upright, inverted and laterally
  inverted mean. Be prepared to use them when
  describing the image formed by a lens or mirror!
• When two real rays meet, a real image is formed
• A real image is one that can be projected onto a
  screen
• When two virtual rays (or a real and a virtual
  ray) meet, a virtual image is formed.

10
A ray through the optical centre
Lens
Object
Principal axis
F
1. A ray is drawn from the tip of the object,
through the OPTICAL CENTRE
11
A ray through the focal point I
Lens
Object
Principal axis
F
2. A second ray is drawn, parallel to the
principal axis, from the tip of the object
to the lens
12
A ray through the focal point II
Lens
Object
Principal axis
F
2. A second ray is drawn, parallel to the
principal axis, from the tip of the object
to the lens
3. A third ray is drawn, from the lens and
through the focal point (F) to where it
crosses the original ray
13
Location of the image
Lens
Object
Principal axis
F
4. The image can now be added. A
perpendicular line is drawn from the
principal axis to where the rays meet.
14
Conclusion
Lens
Object
Principal axis
F
Conclusion By considering the simple case of
two rays of light leaving the same point on an
object, we have been able to determine the
location of the image produced by the lens
15
Drawing ray diagrams virtual image
Lens
Object
Optical Centre
Principal axis
F
F
Principal Focus
Principal Focus
NOTE that the lens is drawn as a straight line
with arrowheads to represent its shape. This is a
convex lens.
16
A ray through the optical centre
Lens
Object
Principal axis
F
F
1. A ray is drawn from the tip of the object,
through the OPTICAL CENTRE
17
A ray through the focal point I
Lens
Object
Principal axis
F
F
2. A second ray is drawn, parallel to the
principal axis, from the tip of the object
to the lens
18
A ray through the focal point II
Lens
Object
Principal axis
F
F
3. A third ray is drawn, from the lens and
through the focal point (F).
19
Virtual rays
Lens
Object
Principal axis
F
F
4. Two virtual rays are drawn behind the lens.
20
Location of the image
Lens
Object
Principal axis
F
F
5. The image can now be added. A
perpendicular line is drawn from the
principal axis to where the rays meet.
21
Conclusion
Lens
Object
Principal axis
F
F
Conclusion By considering the simple case of
two rays of light leaving the same point on an
object, we have been able to determine the
location of the image produced by the lens
22
Diverging Lens Step 1
Lens
Object
Principal axis
F
F
1. Draw a ray from the tip of the object to the
lens, parallel to the principal axis.
23
Diverging Lens Step 2
Lens
Object
Principal axis
F
F
2. To draw the continuation of this ray we use
the focal point on the left of the lens to plot
the path of the virtual ray which becomes a real
ray on the right of the lens.
24
Diverging Lens Step 3
Lens
Object
Principal axis
F
F
3. Do the usual with the second ray straight
from the tip of the object through the optical
centre.
25
Diverging Lens Step 4
Lens
Object
Principal axis
Image
F
F
4. The image is formed at the intersection of the
virtual ray and the real one.
26
Diverging Lens - Conclusion
Lens
Object
Principal axis
Image
F
F
Conclusion By considering the simple case of
two rays of light leaving the same point on an
object, we have been able to determine the
location of the image produced by the lens
27
Mirrors Convex Concave
Convex Mirror
Concave Mirror
28
Convex Mirror I
Convex Mirror
Object
Principal axis
F
F
1. A ray is drawn from the tip of the object,
parallel to the principal axis to the mirror
29
Convex Mirror II
Convex Mirror
Object
Principal axis
F
F
2. A reflected ray is drawn using the focal
point behind the mirror, using dotted lines to
show the path of the virtual rays.
30
Convex Mirror III
Convex Mirror
Object
Principal axis
F
F
3. A ray is drawn to the pole or centre of the
mirror and the reflected ray is drawn (using
ir). The ray is continued behind the mirror,
using dotted lines to show the path of the
virtual rays.
31
Location of Image
Convex Mirror
Object
Principal axis
F
F
4. The intersection of the virtual rays gives us
the location of the virtual image.
32
Concave Mirror I
Concave Mirror
Object
Principal axis
F
F
1. A ray is drawn from the tip of the object,
parallel to the principal axis to the mirror.
33
Concave Mirror II
Concave Mirror
Object
Principal axis
F
F
2. The ray is reflected back through the focal
point.
34
Concave Mirror III
Concave Mirror
Object
Principal axis
F
F
3. Another ray is drawn, this time to the pole or
centre of the mirror. The reflected ray obeys
ir.
35
Location of Image
Concave Mirror
Object
Principal axis
F
F
4. If the object is between F and the mirror a
virtualimage is produced, behind the mirror.
Useful for shaving! If the object is moved
outside F try it for yourselves!