grade 8 science unit 2: optics show... · grade 8 science unit 2: optics chapter 6: lenses refract...
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Grade 8 Science
Unit 2: Optics
Chapter 6:
Lenses refract light to form images.
Lenses
A curved piece of
transparent material that
refracts light in a
predictable way.
Usually made from glass or
plastic.
Lense
s
There are two types of lenses:
1. Convex
Centre of the lens bulges out
Causes light rays to bend toward each other (converge)
2. Concave
Centre of the lens is curved
in
Causes light rays to bend
away from each other
(diverge)
Conve
x v
s. C
onca
ve L
ense
s
Convex Lenses
Can act as a magnifying
glass
Each lens has its own focal
length (the distance from
the centre of the lens to
the focal point)
The greater the curvature of the lens, the shorter the focal length. (pg. 217)
Lenses have focal points on either side because light shines through either side.
The line through the centre of the lens is called the principle axis.
Optical centre is where the principle axis meets the lens centre.
Principle
Axis
Optical
Centre
Concave Lenses
To find the focal point, you
must extend the refracted
rays back.
Lenses with the greater
curvature have the shortest
focal length. (pg. 221)
Corrective Lenses
The Eye (pg. 229)
Vis
ion
Near-sighted Vision
See objects up close but
not at a distance.
Concave lenses are used to
correct this vision.
Near
-si
ghte
d V
isio
n
Far-sighted Vision
See objects at a distance
but not up close.
Convex lenses are used to
correct this vision.
Far
-sig
hte
d V
isio
n
Dete
rmin
ing
Foca
l Lengt
h... You must include
the following
incident rays:
1. Travelling
parallel to
the p.a.
2. Travelling
through the
o.c.
3. Travelling
through the F.
Ray Diagrams: Convex Lenses
Object between the lens and
focal point.
Object is between the focal
point and 2X the focal
length.
Object is more than 2X the
focal length.
Ray Diagrams: Concave Lenses
The above is true for an object in all
positions.
CORE
STSE:
“Fibre
Optics”Fibre Cable
Optical Technologies...
1. Microscopes
Uses two convex lenses
with relatively short focal
points to magnify
Magnified twice to
increase enlargement
The M
icro
scope
2. Telescopes
The objective lens has a
longer focal length than the
microscope.
Can have either a refracting
or reflecting telescope
Refracting Telescope (pg. 245)
The lenses bend light to
focus it.
The objective lens must be
as large as possible to view
distant galaxies (makes it
heavy)
Reflecting Telescope (pg. 246)
Uses a concave mirror, plane mirror and a convex lens to collect and focus light from objects at a great distance.
Most large telescopes are this type.
The Hubble Space Telescope
Launched in 1990
The Reflecting
Telescope
3. Cameras (pg. 248)
4. Binoculars (pg. 247)
5. Face shields
6. Magnifying glasses
7. Contact lenses
8. Flashlights
9. Eye glasses
The Nature of Science
The development of new technologies involve many individuals and groups of people.
These technologies can alter what we know about the nature of science.
1602
1672
Individuals...
Galileo
Newton
Groups...
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