Download WileyPLUS Assignment 3 is Available Week of March 9

WileyPLUS Assignment 3 is Available
Chapters 21, 22, 24, 25
Due Thursday, March 11 at 11 pm
Week of March 9-11
Experiment 4: Geometrical Optics
Monday, March 8, 2010
66
Thin lens equation
1
ho
3
!
!
!
!
1
3
f
Object distance
Thin lens equation:
Image distance
1 1 1
+ =
do di f
Linear magnification: m =
Monday, March 8, 2010
hi
di
=−
ho
do
67
Conventions for the thin lens equation
Draw ray diagrams with rays travelling from left to right.
Normal situation:
Object
Real object to
left of lens,
object distance
do is positive
Lens
Image
Real image to right
of lens,
image distance
di is positive
Virtual object to right of lens, do is negative (2 or more lenses)
Virtual image to left of lens, di is negative
Converging (positive) lens, focal length f is positive
Diverging (negative) lens, focal length f is negative
Monday, March 8, 2010
68
Example: A 1.7 m tall person stands 2.5 m in front of a camera. The
focal length of the lens is 0.05 m.
a) Find the image distance
b) Find the magnification and the height of the image on the film.
a) di = 51 mm, real image
b) m = -0.0204, hi = -35 mm
Monday, March 8, 2010
69
Prob. 26.54/50: To focus a camera on objects at different
distances, the converging lens is moved toward or away from the
film, so a sharp image always falls on the film.
A camera with a lens of focal length f = 200 mm is to be focussed
on an object located at a distance of 3.5 m and then at 50 m.
Over what distance must the lens be movable?
11.3 mm
Monday, March 8, 2010
70
Clicker Question
An object is located a distance do in front of a lens. The lens
produces an upright image that is twice as tall as the object.
What kind of lens is it? What is the image distance, di ?
A) Converging lens, di = 2do
B) Converging lens, di = -2do
C) Diverging lens, di = 2do
D) Diverging lens, di = -2do
E) Diverging lens, di = do/2
B) Must be a virtual image at twice the object distance.
That is, di = -2do and f > 0 (converging lens) from thin lens
equation.
Monday, March 8, 2010
71
Combinations of lenses – microscope
• Find the location of the image formed by the first lens as if the second
lens did not exist.
• Use that image as an object (source of light) for the second lens using the
sign convention for real and virtual objects.
1
3´
2
3
1´
2
Lens 2: light appears to come
from intermediate image
A microscope producing a virtual, inverted and magnified
final image. The eyepiece acts as a magnifying glass.
Monday, March 8, 2010
72
Prob. 26.65/59: Two identical diverging lenses are separated by 16
cm. The focal length of each lens is –8 cm. An object is located 4 cm
to the left of the lens that is on the left. Determine the final image
distance relative to the lens on the right.
di2 = -5.6 cm, virtual image, to left of lens 2
Monday, March 8, 2010
73
26.-/66: Two converging lenses (f1 = 9 cm, f2 = 6 cm) are separated
by 18 cm. The lens on the left has the longer focal length. An object
stands 12 cm to the left of the left-hand lens.
a) Locate the final image relative to the lens on the right.
b) Obtain the overall magnification.
c) Is the final image real or virtual, upright or inverted, larger or
smaller than the object?
a) di2 = 4.5 cm, real image, to right of lens 2
b) m = m1m2 = -0.75
c) Real, inverted, 0.75 times as large as object
Monday, March 8, 2010
74
Thin Lens
Thin lens equation:
1 1 1
+ =
do di
f
Linear magnification: m =
hi
di
=−
ho
do
do = object distance
ho = height of object
di = image distance
hi = height of image
f = focal length of lens
Two Lenses
Overall linear magnification, m = m1 m2
Monday, March 8, 2010
75
The Human Eye, from above
n = 1.33-1.34
n = 1.38
Most of the
refraction occurs at
the cornea
n = 1.41-1.45
n = 1.34
Blind spot
Sharpest
image, best
colour
discrimination
Biomedical Applications of
Introductory Physics, Tuszynski &
Dixon
Monday, March 8, 2010
76
Existence of the blind spot
(Zinke-Allmang, Physics for the Life Sciences)
6 cm on
printed page
The blue dot
(~140 off axis)
Monday, March 8, 2010
77
The human eye
The eye focuses an image onto the retina by adjusting the focal
length of the eye lens. This is known as accommodation.
Eye lens has its
Ciliary muscle,
relaxed
longest focal length
Greatest distance at which eye can focus: “far point”
Normal value: infinity
Eye lens compressed,
focal length decreased
Closest distance at which eye can focus: “near point”
Normal value: N = 25 cm
Monday, March 8, 2010
78
Nearsightedness
Objects in focus
The eye lens forms an image of a distant object in front
of the retina ! blurred image on the retina
Correction is with a diverging lens that moves the image back
onto the retina. The corrective lens forms a virtual image in
front of the eye that is close enough for the eye to focus on.
Monday, March 8, 2010
79
Farsightedness
Objects in
focus
The eye lens forms an image of a nearby object
behind the retina blurred image on the retina
Correct with a converging lens that forms a virtual
image far enough away for the eye to focus on.
Monday, March 8, 2010
80
Correction of near and farsightedness
Use a corrective lens to form a virtual image at a distance at
which the eye can focus.
Nearsighted:
• The corrective lens forms an image of a distant object at the
person’s far point, or closer.
Farsighted:
• The corrective lens forms an image of a nearby object at the
person’s near point, or further.
Power of a lens:
• Power is 1/f, focal length in metres, power in diopters.
Example, f = –10 cm, power = 1/(– 0.1) = –10 diopters.
Monday, March 8, 2010
81