Grade 8 Science Unit 2: Optics

1
Grade 8 ScienceUnit 2 Optics

• Chapter 6
• Lenses refract light to form images.

2
Lenses

• A curved piece of transparent material that
  refracts light in a predictable way.
• Usually made from glass or plastic.

3
Lenses
4

• There are two types of lenses
• 1. Convex
• Centre of the lens bulges out
• Causes light rays to bend toward each other
  (converge)

5

• 2. Concave
• Centre of the lens is curved in
• Causes light rays to bend away from each other
  (diverge)

6
Convex vs. Concave Lenses
7
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)

8

• The greater the curvature of the lens, the
  shorter the focal length. (pg. 217)

9

• 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.

10
Optical Centre
Principle Axis
11
Concave Lenses

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

12

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

13
Corrective Lenses
The Eye (pg. 229)
14
Vision
15
Near-sighted Vision

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

16
Near- sighted Vision
17
Far-sighted Vision

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

18
Far-sighted Vision
19

• You must include the following incident rays
• Travelling parallel to the p.a.
• Travelling through the o.c.
• Travelling through the F.

Determining Focal Length...
20
Ray Diagrams Convex Lenses

• Object between the lens and focal point.

21

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

22

• Object is more than 2X the focal length.

23
Ray Diagrams Concave Lenses
The above is true for an object in all positions.
24
CORESTSEFibre Optics

• Fibre Cable

25
Optical Technologies...

• 1. Microscopes
• Uses two convex lenses with relatively short
  focal points to magnify
• Magnified twice to increase enlargement

26
The Microscope
27

• 2. Telescopes
• The objective lens has a longer focal length than
  the microscope.
• Can have either a refracting or reflecting
  telescope

28
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)

29
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.

30

• The Hubble Space Telescope

Launched in 1990
31
(No Transcript)
32

• 3. Cameras (pg. 248)
• 4. Binoculars (pg. 247)
• 5. Face shields
• 6. Magnifying glasses
• 7. Contact lenses
• 8. Flashlights
• 9. Eye glasses

33
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.

34
Individuals...
Galileo
Newton
35
Groups...