PHY138 – Last Waves Lecture
Today’s overview
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Curved Refracting Surfaces: Lenses
Lens Aberrations
Thin Lens Equation
Corrective Optics
Introduction to Kimberly Strong and
Electromagnetism Quarter
Reading Assignment
Today’s reading assignment from the text by
Knight was:
Chapter 23, Sections 23.7 and 23.8
(This material is part of the course, and may
appear on the final exam in April)
Suggested Chapter 23 Exercises and
Problems for Practice: 31, 73, 81
Reading Assignment for January, 2006
Between now and January 9, please read
Chapter 25, “Electric Charges and Forces”,
Sections 25.1-25.6.
There will be a masteringphysics Pre-Class
quiz on Chapter 25 material, due Mon. Jan 9
by 10:00 AM.
Lenses
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Formed by two curved boundaries between
transparent media.
Lenses may have spherical surfaces (lensmaker’s equation). Most modern lenses have
non-spherical curved surfaces to avoid
spherical aberration.
Every lens has a diameter, D, and focal
length, f.
The ratio of (f / D) is called “f-number”. For
example, an “f/6” lens has a focal length of 6
times its diameter.
Diverging rays through a Converging Lens
Focal length, f
This follows from the principle of reversibility.
Quiz 1
f
What will happen to the rays emerging to the
right of the lens if the face is moved a little
closer to the lens?
1. They will remain parallel.
2. They will diverge (spread out).
3. They will converge (toward a focus).
Quiz 2
f
What will happen to the rays emerging to the
right of the lens if the face is moved a little
further away from the lens?
1. They will remain parallel.
2. They will diverge (spread out).
3. They will converge (toward a focus).
Diverging rays through a Converging Lens
Focal length, f
s’
s
1 1 1
 
s s' f
Thin Lens Equation: sign conventions
image
object
f
s
1 1 1
 
s s' f
s’
s is positive for objects to the left of lens, negative
for objects to the right of lens (virtual objects).
s’ is positive for images to the right of lens, negative
for images to the left of lens (virtual images).
f is positive for converging lenses, negative for
diverging lenses.
The human eye
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A near spheroid, about 22 mm from cornea to
retina.
Focal length is 17 mm in relaxed state
(distant vision)
Focal length is 14 mm in tensed state (near
vision)
“Near Point” is about 25 cm for a normal eye.
“Far Point” is infinity for a normal eye.
Corrective Optics 1
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Myopia is when the far point is less than
infinity. (“near-sighted”)
The Myopic “near point” is usually closer than
25 cm.
A diverging lens moves the far point out to
infinity, allowing for a crisp focus of distant
objects.
Corrective Optics 2
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Hyperopia is when the near point is signficantly
greater than 25 cm. (“far-sightedness”)
The relaxed hyperoptic eye does not focus at
infinity. By tensing the eye, distant objects can
be seen.
A converging lens moves the near point closer
and allows distant objects to be seen with a
relaxed eye.
Many people develop hyperopia in their 40s or
50s.
“Men and women are not content to comfort
themselves with tales of gods and giants, or
to confine their thoughts to the daily affairs
of life; they also build telescopes and
satellites and accelerators, and sit at desks
for endless hours working out the meaning
of the data they gather.”
… Steven Weinberg
(Nobel Prize in Physics 1979)
PHY138 – Electromagnetism
Lecture 0
• New instructor: Prof. Kimberly Strong
• Room: MP710A
• Email: strong@atmosp.physics.utoronto.ca
• 6 weeks: January 9 to February 17, 2006
In-Class Quiz
When I grow up, I want to be:
1. A doctor
2. A physicist
3. A scientist (but NOT a physicist)
4. None of the above
5. I don’t know
In-Class Quiz
When I grow up, I want to be:
1. A doctor
2. A physicist
3. A scientist (but NOT a physicist)
4. None of the above
5. I don’t know
6. Any of the above!
Syllabus for Q3 - Electromagnetism
(parts of) Chapters 25 to 33
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Electric Forces and Electric Fields
Electric Potential Energy
The Electric Potential
Equipotentials and Energy in Capacitors
Currents, Resistance, and Resistivity
Circuits and Kirchoff’s Laws
Magnetic Fields and Magnetic Force
Electromagnetic Inductors
Dates to Remember for the First Week
of Q3 ...
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The first week’s reading assignment is
Chapter 25 of Knight, Sections 25.1 to 25.6
10:00 AM, Monday, January 9:
Finish the first Mastering Physics pre-class
quiz on this reading assignment
11 AM, Monday, January 9:
Our first lecture of 2006 here in Con. Hall
11:59 PM on Friday, January 13:
Finish the first MP problem set
Have a great break!
(and read Chapter 25)
See you on January 9