This document provides an overview of physical and geometric optics. It discusses geometric ray optics which uses reflection and refraction to understand image formation. Geometric optics is accurate when light wavelengths are smaller than object dimensions. Wave physical optics considers interference between waves travelling different paths and can be used for any electromagnetic radiation. The document asks questions about using x-rays and infrared for medical imaging applications and explains the appropriate approach based on geometric or physical optics. It also covers thin lenses, mirrors, and how changing lens properties affects image formation.

1. Physical and geometric optics
Learning object 8
- Zeanna Janmohamed
Figure 1.0 optics diagram: http://4.bp.blogspot.com/-u-
JvAmYr8dQ/VL6O4xnORXI/AAAAAAAAAl8/jaHgHuld-w8/s1600/convex_sign_convention.png

2. Geometric ray optics
• A branch of physics that uses reglcyion and
refraction to understan how images are
formed
– Upsides? Its accurate as long as the wavelength of
the light is smaller than the dimensions of the
object
– What happens when we can no longer use ray
optics?
• New field is developed!

3. Wave physical optics
• Used when conisdering the interference
between waves travelling in different paths
• Can be used for any electromagetic radiation
(not only light, but because light has large
wavelengths it is easier to use)
Figure 1.1 electromagnetic
spectrum
http://www.yorku.ca/eye/sp
ectrum.gif

4. Check and reflect
• Question 1. Is it appropriate to
use x-rays for visualizing your
intermediate phlanges (a bone
in your finger)? How can you
explain why by using gemetric
optics or physical optics.
• Question 2. Is it appropriate to
useinfared to shine on a red
blood cell? How can you
explain why by using gemetric
optics or physical optics.
Figure 1.3 intermediate phalanges
http://upload.wikimedia.org/wikipedia/commons/1/11/Intermedia
te_phalanges_of_the_hand_(left_hand)_02_dorsal_view.png
Figure 1.4 red blood cell
http://news.rice.edu/wp-
content/uploads/2012/09/0914_BLOOD_lg.jpg

5. Check and reflect answers
1. Yes it is appropriate. We can surmize this because the
size of your intermediate phalange is between 2-6cm,
and x rays are considerably smaller at 0.01 o 10nm,
and therefore gemetric optics can be used to evalute
this problem.
2. No it is not appropriate, although it can be done. We
can surmize this because the size of your blood cells
are around 8 micrometers in width. Comparivley, infa
rays are between 0.7 to 300 micrometers, and are
similar, if not larger to the red blood cells. Therefore
you must use physical optics to analyse the situation

6. Geometrical optics = thin lenses
• A lense is a refracting device = redistribues the
energy that is propagated by the EMR
• Converging or convex lenses are thicker at
their midpoint and taper off at the end
• Diverging or concave lenses are thicker at their
ends and thin down at the middle
Figure 1.6 converging and diverging
lenses
http://www.physicsclassroom.com/Cla
ss/refrn/u14l5a1.gif

7. Geometrical optics = thin lenses cont.
• Lenses that have two surfaces are known as
simple
• If the thickness is negligible compared to the
overall path of light the lenses are called thin
• the formula for the lens is now:
– N1 = index of refraction, R2 = radius of curvature
of left surface, r2 = radius of curvature of right
surface
Figure 1.7 lens format
http://www.sparknotes.com/physics/opti
cs/geom/section3.rhtml

8. Geometric optics= mirrors
• Concave mirrors = reflect the incoming waves
to a focal point in front of the mirror
• Convex mirrors = reflect incomping waves
outwards so that the image appears behind
the mirror
Figure 1.8 concave and
convex mirrors
http://buphy.bu.edu/~duffy
/PY106/22c.GIF

9. Further analysis
• Follow this link and see how the images are
formed by converging lesnes. Observe how
changing the radius and the refractive index of
the lenses affects the image that is formed (what
do you notice? Do they follow the patterns
explained by converging or diverging lenses )
• http://phet.colorado.edu/en/simulation/geometr
ic-optics