Transcript q - BYU Physics and Astronomy

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Discussion question: A fish swims below the
surface of the water. The observer sees the
fish at
A greater depth than it really is
B. The same depth
C. A smaller depth than it really is.
A.
Imaging Assumptions
“Thin Lens” approximation
 Diameter of lens/mirror is much larger
than the wavelength of light
– This lets us do ray approximations
– We’ll discuss what happens if this isn’t
true later
 Aberations

Making Images with Lenses and
Mirrors
Conventions for Imaging
Calculations

The Principal or Optical Axis
– It is a line drawn from + infinity to – infinity
which passes through the center of the
lens/mirror and is normal to the surface of the
lens/mirror at its center.
Conventions for Imaging
Calculations

p=distance from the object to lens or mirror along
principle axis
– p is usually positive...
– but p is sometime negative (when I have a “virtual
object” as in the case for the second lens below).
-p
p
Conventions for Imaging
Calculations

q = distance from the lens or mirror to the image
– Measured using a “ruler” which is parallel to the optical
axis.
q
Conventions for Imaging
Calculations

q = distance from the lens or mirror to the image
– Measured using a “ruler” which is parallel to the optical
axis.
– q is positive if the image is on the side of the lens or
mirror where we expect the light to go. In this case we
say that the image is real.
Conventions for Imaging
Calculations

q = distance from the lens or mirror to the image
– q is negative if the image forms on the side of the lens
or mirror where the light doesn’t really go. In this case
we say that the image is virtual.
-q
Is the image you see when you
look in the mirror real or virtual?
A.
B.
C.
D.
E.
Real
Virtual
Yes
Why?
42
Images Formed by a Flat Mirror
Is the image in a flat mirror real or virtual?
Is q for a flat mirror negative or positive?
Conventions for Imaging
Calculations

M = the lateral magnification of the image
– M=image height / object height
– M is negative if the image is inverted
– For a flat mirror, M is always 1

f = the focal length of a mirror or lens
– If f is positive, it is the distance from the mirror/lens
that collimated light passing through it is focused to.
– If f is negative, it is the distance away from the
mirror/lens of a spot that light appears to be
diverging from when collimated light passes through
Negative and Positive f Mirrors
f
-f
Finding the Focal Length of a
Concave Mirror
F=R/2
θ
θ
θ
Finding the Focal Length of a
Convex Mirror
F=-R/2
Let us be of good cheer as we go about our lives. Although
we live in increasingly perilous times, the Lord loves us and
is mindful of us. He is always on our side as we do what is
right. He will help us in time of need. Difficulties come into
our lives, problems we do not anticipate and which we
would never choose. None of us is immune. The purpose of
mortality is to learn and to grow to be more like our Father,
and it is often during the difficult times that we learn the
most, as painful as the lessons may be. Our lives can also
be filled with joy as we follow the teachings of the gospel
of Jesus Christ.
-- President Thomas S. Monson, General Conference,
October 2012
Finding Image Location and
Magnification by Drawing Lines
R
Finding Image Location and
Magnification with Equations
The Mirror/Lens Equation,
Magnification
How far from a converging mirror should I put an
object if the mirror has a radius of curvature of
1 meter and I want the image to be the same
size as the object?
A : less than 0.25 m
B : 0.25 m to 0.75 m
C : 0.75 m to 1.25 m
D : 1.25 m to 3 m
E : more than 3 m
I look at my image in a round Christmas
ornament. Which of the following will be true?
A : The image will be upright (not inverted) and
real.
B : The image will be upright and virtual.
C : The image will be inverted and real.
D : The image will be inverted and virtual.
E : The ornament will shatter.