Grade 8 ScienceGrade 8 ScienceGrade 8 ScienceGrade 8 ScienceUnit 2: OpticsUnit 2: Opticspp

Chapter 6:Lenses refract light to f rm ima esform images.

LensesLensesLensesLensesA curved piece of A curved piece of transparent material that prefracts light in a

di bl predictable way.Usually made from glass or Usually made from glass or plastic.p

esen

seLe

There are two types of llenses:

1 Convex1. Convex Centre of the lens bulges g

outC li ht t b d Causes light rays to bend toward each other (converge)

2. Concave2. ConcaveCentre of the lens is curved inC l h b d Causes light rays to bend away from each other away from each other (diverge)( g )

esLe

nse

ave

LC

onc

vs. C

nvex

C

on

Convex LensesConvex LensesConvex LensesConvex Lenses

Can act as a magnifying Can act as a magnifying glassgEach lens has its own focal length (the distance from the centre of the lens to the centre of the lens to the focal point)p )

The greater the curvature f h l h h h of the lens, the shorter the

focal length. (pg. 217)focal length. (pg. 217)

Lenses have focal points on peither side because light shines thro h either side shines through either side. The line through the centre The line through the centre of the lens is called the

i i l iprinciple axis.Optical centre is where the Optical centre is where the principle axis meets the lens centre.

O i l Optical CentreCentre

Principle pAxis

Concave LensesConcave LensesConcave LensesConcave Lenses

To find the focal point you To find the focal point, you must extend the refracted rays back.

Lenses with the greater Lenses with the greater curvature have the shortest focal length. (pg. 221)

Corrective LensesCorrective LensesCorrective LensesCorrective Lenses

The Eye (pg. 229)

nis

ion

Vi

NearNear--sighted Visionsighted VisionNearNear sighted Visionsighted Vision

See objects up close but See objects up close but not at a distance.Concave lenses are used to correct this vision.

ion

d V

isi

hted

-si

ghN

ear-

N

FarFar--sighted Visionsighted VisionFarFar sighted Visionsighted Vision

See objects at a distance See objects at a distance but not up close.pConvex lenses are used to correct this vision.

sion

d V

isgh

ted

ar-s

igFa

h... You must include

h f ll i en

gth the following incident rays:

al L

e 1. Travelling parallel to

Foc

a pthe p.a.

2 Travelling

inin

g 2. Travelling through the o c

erm

i o.c.3. Travelling

h h h F

Det through the F.

Ray Diagrams: Convex LensesRay Diagrams: Convex LensesRay Diagrams: Convex LensesRay Diagrams: Convex Lenses

Object between the lens and Object between the lens and focal point.p

Object is between the focal Object is between the focal point and 2X the focal length.

Object is more than 2X the Object is more than 2X the focal length.

Ray Diagrams: Concave LensesRay Diagrams: Concave LensesRay Diagrams: Concave LensesRay Diagrams: Concave Lenses

The above is true for an object in all The above is true for an object in all positions.

CORESTSESTSE:“Fibre Fibre Optics”

Fib C blp

Fibre Cable

Optical TechnologiesOptical TechnologiesOptical Technologies...Optical Technologies...

1 Microscopes1. Microscopes Uses two convex lenses

with relatively short focal points to magnify

Magnified twice to Magnified twice to increase enlargementincrease enlargement

ope

osco

Mic

roT

he M

T

2. Telescopes2. TelescopesThe objective lens has a longer focal length than the

imicroscope.Can have either a refracting Can have either a refracting or reflecting telescopeg p

Refracting Telescope (pg 245)Refracting Telescope (pg 245)Refracting Telescope (pg. 245)Refracting Telescope (pg. 245)

The lenses bend light to The lenses bend light to focus it.The objective lens must be as large as possible to view distant galaxies (makes it distant galaxies (makes it heavy)y)

Reflecting Telescope (pg 246)Reflecting Telescope (pg 246)Reflecting Telescope (pg. 246)Reflecting Telescope (pg. 246)

Uses a concave mirror, Uses a concave mirror, plane mirror and a convex l ll d f lens to collect and focus light from objects at a great light from objects at a great distance.Most large telescopes are this typethis type.

The Hubble Space Telescopep p

Launched in 1990Launched in 1990

The Reflecting The Reflecting Telescope

3. Cameras (pg. 248)(pg )4. Binoculars (pg. 247)5. Face shields6 M f l6. Magnifying glasses7 Contact lenses7. Contact lenses8. Flashlights8. Flashlights9. Eye glassesy g

The Nature of ScienceThe Nature of ScienceThe Nature of ScienceThe Nature of Science

The development of new The development of new technologies involve many i di id l d f individuals and groups of people.people.These technologies can alter what we know about the nature of sciencethe nature of science.

Individuals...

1602

1672Galileo

1672

NNewton

Groups...