Download Unit #3 - Optics Activity: D21 Observing Lenses (pg. 449) Lenses

ist10_ch11.qxd
Unit #3 - Optics
11.3 Lenses
7/22/09
3:53 PM
Page 449
Night vision goggles use lenses to focus light onto a device called an
image intensifier. Inside the intensifier, the light energy releases a
stream of particles. These particles then hit a phosphor-coated screen.
The phosphors glow when the particles strike them. The person
wearing the goggles sees a glowing green image (Figure 11.47).
Activity: D21
Observing Lenses (pg. 449)
Figure 11.47 The image intensifier of night goggles amplifies the particles before they hit the
screen. The image appears as shades of green.
D21 Quick Lab
Observing Lenses
Purpose
Procedure
To observe how concave and convex lenses affect
light
1. Look though each lens at the printed text in this
student book. Record your observations.
2. Look through both lenses at some printed text.
Record your observations.
Materials & Equipment
• convex lens (bulges
out)
• screen, such as a
piece of paper
• concave lens (middle is
thinner than the edges)
• candle holder, such as
sand and a metal tray
3. Try to use each of the lenses to project a candle
flame or light onto a screen or piece of paper.
Record your observations.
Questions
• light source, such as a
candle
4. Which single lens would be most useful as a
magnifying glass?
CAUTION: If an open flame is used, it must be secured so
that it cannot fall over. Keep all combustible materials
away from open flames. Tie back long hair before using
an open flame.
5. How should the convex and concave lenses be
arranged to make a distant object appear closer?
6. What arrangement of lenses is most effective in
projecting the image of a light source onto a
piece of paper?
Ray diagrams model the behaviour of light in mirrors and lenses.
Lenses
curved transparent material that is smooth and
regularly shaped
transparent glass or very hard plastic
thin lens
strong, hard, polished
‣
rays converge or diverge
can magnify the image
image produced by a thin lens can be real or virtual,
inverted or upright, larger or smaller.
thickness is slight compared to its focal length
449
image.
sides of the lens, it is possible to make light rays diverge or converge as
converging and diverging,
depending on how they refract
the light that enters them.
they pass through the lens. The most important aspect of lenses is that
the light rays that refract through them can be used to magnify images
or to project images onto a screen. Relative to the object, the image
produced by a thin lens can be real or virtual, inverted or upright, larger
or smaller.
sed
Lens Terminology
Figure 11.50 illustrates some o
converging and diverging lense
Two
RayTypes
Diagram
diverging lenses
(thinnest in the middle)
converging lenses
(thickest in the middle)
asses
n be
eg, use
refract
erties
m.
hese
d in
ray 1
object
ray 2
(a)
Define: (pg. 450)
‣
axis of symmetry
‣
focal point (x 2) (F)
‣
focal length ( )
principal
F axis
F´
principle axis
‣
• The pri
through
surface
axis of symmetry
f
• Both ki
The foc
focus or
the sym
the lens
f
(b)
principal
F´ axis
F
axis of symmetry
f
f
Figure 11.50 (a) Converging lens and (b) diverging lens
Lens Terminology
F
image
450
UNIT D
• The ax
line dra
• The foc
of symm
along th
same w
lens, bo
focal len
Light and Geometric Optics
Figure 11.50 illustrates some of the terms associated with both
converging and diverging lenses:
• The principal axis is an imaginary line drawn
through the optical centre perpendicular to both
surfaces.
• TheLenses
axis of symmetry is an imaginary vertical
Concave
principal
F axis
line drawn through the optical centre of a lens.
• Both kinds of lenses have two principal focuses.
aka: diverging lens
The focal point where the light either comes to a
light is refracted
away
focus
or appears to diverge from a focus is given
from the principle axis
the symbol F, while that on the opposite side of
‣ rays will never meet
the lens is represented by F!.
ist10_ch11.qxd
7/22/09
3:53 PM
Uses
‣
eyeglasses have one
convex surface and
one concave surface
understanding how
m a lens. The index
‣ telescopes and
binoculars use
on other
side
refraction
of
air.
concave lenses to
principal
• The focal length, f, is the distance from the axis
F´‣ axis
improve the detail
Image: smaller,
of symmetry to the principal focus measured
into the upright,
lens,virtual
the
along the principal axis. Since light behaves the
rface and toward
(a)direction through a
(b)
same way travelling in either
both types of thin lenses have two equal
f
at
an angle, thelens,
light
focal lengths.
Figure 11.53 (a) Concave lens
diverging lens
he normal. In other
(b) and convex lens
ptics
t on entering the
1.53).
f
Diagrams
Page 452
In yo
thin lens.
compared
lens. You
affecting
the axis o
Drawin
Ray diagr
You need
steps in F
Rules for Ray Diagrams
‣
ray parallel to PA
Ray diagrams model the behaviour of light in mirrors and lenses.
451focal
extends from
point
‣
ray travelling through
centre, in not
refracted (stays
straight)
Image is located at ray
intersection
ray 1
object
ray 2
F
image
Figure 11.54 Concave lens ray diagram
Conve
A conver
the centr
cave Lenses
How the Image Is Used
Homework
for
a types
Lens
Some
of eyeglasses
Ray Diagram
Convex Lenses
Read 448 - 452
rayist10_ch12.qxd
1
telescopesand
make
use
object
rand
predicting
understanding
how
7/22/09 3:56 PM Page 484
aka: converging lens
Draw a diverging lens with a focal point of 4 cm, and
of the diverging
properties
draw image at these situations:
ays
emerging
from
a lens. The index
light is refracted
of concave
lenses.
These
toward the principle
An Object which is 2 cm tall and 8 cm from the
ray 2
axis
han
of refraction
of air.
axis of symmetry
lensesthe
areindex
often
used
in
An with
Object 4 cm tall and 2 cm from the A of S
ycombination
passes from
air into the lens, the
F image
converging lenses.
from the lens surface and toward
(a)
(b)
Cameras
Our view of ourselves, ou
es out of the lens at an angle, the light
Figure 11.53 (a) Concave enormously
lens
by learning h
ding away from the normal. In other
optics have allowed us to
(b) and convex lens
Microscopes have allowe
fractions, the first on entering the
that was completely unk
Activity: D24 - Focal Length
telescopes, we have obse
he lens (Figure 11.53).
‣
-
-
for a (pg.
Lens
459)
r predicting and understanding
how
Ray diagrams model
the behaviour
ays emerging from a lens. The index
steps 2-9
han theRead
index
of refraction of air.
y passes from air into the lens, the
from the lens surface and toward
es out of the lens at an angle, the light
ding away from the normal. In other
fractions, the first on entering the
he lens (Figure 11.53).
outshining nearby galaxi
images of all these very l
Object outside FP
recent increased
of
light in mirrors and lenses. The451
‣ image is real;
power cameras has had i
inverted
incorporated into cellpho
Object inside FP
taken almost anywhere a
‣ image is virtual;
around the world. This w
upright
about privacy, but it has
communities of people in
(a)
(b)Cameras are also use
vision systems to ensure
Figure 12.24 This portable imaging
device is equipped with a
the Canadian Food Inspe
Figure
(a) Concave
lens
head-mount11.53
display for inspecting
the
to monitor food colour a
sanitation
of food-processing
(b)
and
convex lens
food. If the colour of the
equipment.
stored value, an alarm go
inspected.
Parts
diaphragm
focussing ring
‣
camera
‣
projectors
‣
magnifying glass
451
A came
one end
aperture
detecto
image (on film)
For a di
shutter
lens
object
the foca
must be
do
di
the ima
length o
Figure 12.25 The parts of a simple camera that uses film
the par
aperture is the opening
Suggested Activity •
the iris controls the pupi
D32 Inquiry Activity on page 493
in low light situations or
The larger the aperture, t
Ray diagrams model the behaviour of light in mirrors and lenses.
Uses
film spool
film
from the lens, it passes through the principal
2. The second ray travels from the tip of the ob
optical centre of the lens and is not refracted
3. Draw the real image where the rays appear t
Rules for Ray Diagrams
Diagrams
‣
ray parallel to PA
travels through F
‣
ray travelling through
centre, in not
refracted (stays
straight)
Suggested Activity •
D25 Inquiry Activity on page 460
‣
ray that goes
through F, stays
parallel
object
ray 1
ray 2
F image
Figure 11.58 Convex lens ray diagram
Image is located at ray
intersection
Learning Checkpoint
1. Describe the difference in shape between a convex lens
2. Which lens, convex or concave, can also be called a div
Activity: D26 - Identifying the
Properties of Images
3. Why do light rays bend twice when lenses are used?
4. DrawEquation
a ray diagram for a convex lens when the object is
Thin Lens
(a) more than two focal lengths away from the lens
(b) exactly two focal lengths from the lens
Handout
Focal Length ( )
pg 461
distance of object (do)
‣
1 = 1 + 1
Thin Lens Equationd
Qu # 10
distance of image (di)
o
di
The distance of the object from the lens, do, the dista
from the lens, di, and the focal length of a lens, f , ca
using the thin lens equation. Given any two of the
can use the thin lens equation to solve for the third:
1
1
1
=
+
f
do
di
Remember that:
454
UNIT D
‣
A concave lens has a negative focal length and a
negative distance to the image.
‣
A convex lens has a positive focal length and either
a positive or negative distance to the image,
depending where the object is placed.
‣
The image distance di is positive if the image is real
and negative if the image is virtual.
Light and Geometric Optics
A convex lens has a focal length of 60.0 cm. A candle
is placed 50 cm from the lens. What type of image is
formed, and how far is the image from the lens?
Example:
‣
A convex lens of a magnifying glass is held 2.00 cm
above a page to magnify the print. If the image
produced by the lens is 3.60 cm away and virtual,
what is the focal length of the magnifying glass?
Activity: D26 - Identifying the
Properties of Images
Handout
pg 461
‣
Qu # 10
A camera with a 200 mm lens makes a real image of a
bird on film. The film is located 201 mm behind the
lens. Determine the distance from the lens to the bird.
Homework
Read 452 - 458
‣
pg. 461 - Qu # 10, 11, 12
‣
pg. 454 - Qu #1-3
‣
pg. 455-457 - Qu #1 from each group