1. Light and Optics Week 3/4
Ms Deanne
Science 8

2. Lenses and vision
-Describe the difference between concave and convex lenses? (p.208)
What happens to light when it passes through a lens? (p.209)
How does your eye form an image? (p.210)
Identify the similarities and differences between your eye and a camera.
What is accommodation? (p.215)
What is a blind spot? (p.217)

3. Lenses and Vision A lens is a curved piece of transparent material.
Example: glass or plastic
Light refracts as it passes through a lens, causing the rays to bend.

4. Types of Lenses
A Concave Lens is thinner in the center than at the edges.
Light passing through the thicker. More curved areas will bend more Causes rays of light to spread out or diverge

5. Types of Lenses
A Convex lens, is thicker in the middle than around the edges Causes refracting light rays to come together or converge

6. A closer look at Convex Lenses
Since Convex lenses bring light rays together they are very useful:
1)Act as a light collector
2) Forms a real image

7. What are examples of Concave and convex lenses?
Think about it!

8. Eye Spy

9. Ciliary Muscle: Relaxes and tightens the lens
Scelera: keeps the shape and protects the eye
Optic Nerve: Connects eye to the brain. Blind spot
Cornea: thick protective layer. Also used to focus light
Lens: flexible unit used to direct light and focus images
Vitreous Humour: fluid portion
Pupil: hole in the iris that lets light in
Retina: rods/cones. Changes light into electrical signals
Iris: colored ring that controls the size of the pupil
Aqueous humour: fluid filled area. Provides cornea and lens with oxygen and nutirents
Choroid: supplies blood to the retina

10. Evolution of the eye
BL_U&t=40s
Is a blind spot truly a limitation to the human eye? What are some possible advantages and disadvantages of an “inside out” retina?

11. Camera vs. Eye
Light gets through the pupil in the eye and the apeture in a camera.
In the eye the iris controls the amount of light that enters the eye in a camera the diaphragm does this
sciences.com/en/media/6-the-eye
sciences.com/en/media/79-how-does-vision- work

12. Remember… When the Iris gets bigger the pupil gets smaller.
This happens when you are in bright situations
When the iris gets smaller the pupil gets bigger
This happens when you are in dark situations

14. When Light Gets In
In order to see light rays must strike the sensitive retina at the back of the eye
The retina is a special layer that is filled with photoreceptors  cells that are sensitive to light
There are 2 types of photoreceptors:
1) Cones: detect color
2) Rods: detect light

15. Eye See… The process of seeing goes like this:
1) Iris and pupil sense the environment (light or dark) and adapt
2) Light enters the pupil and goes to the retina
3) The Photoreceptors on the retina are stimulated
4) Photoreceptors send message to the optic nerve
5) Optic nerve passes the message on to the brain
6) The brain translates the message into an image

16. Putting it in Focus
In the human eye, the lens cannot move, so the ciliary muscles change the shape of the lens
If the image is close the lens bulges in the middle
If the image is far away the lens stretches
This process of the lens changing shape is called accommodation

17. Think about it! So why do people need glasses?

18. Other Types of Eyes…
Compound Eyes : Insects and crustaceans have compound eyes. Each eye is made up of many smaller units called ommatidium.

19. Eye vs Camera https://www.youtube.com/watch?v=OGqAM2 Mykng
1. As an object moves towards the eye, the lens _____ in order to keep the object in focus.
Changes shape by getting thinner
Changes shape by getting fatter
Moves closer to the retina
Moves away from the retina

20. Eye vs Camera
2. The photoreceptors for color vision in the human eye _____.
Are evenly distributed on the retina (except for the blind spot)
All work at the same speed
Have colored filters on top of them
Are sensitive to different wavelengths of light

21. Eye vs camera
3. When we look directly at a dim star, it can disappear from view because _____.
It goes out of focus so it is too blurry to see
There are no photoreceptors for dim light in the center of the retina
Our eyes jiggle too much in the dark
We have a blind spot where there are no photoreceptors
What improvements or modifications can you suggest to either existing cameras or to the human eye?

22. Pinhole Camera
Flip to the assignment page in your booklet!

23. Extending Human Vision
Describe the difference between a reflecting and a refracting telescope (p.221)
How are prisms used in binoculars? (p.223)
How has the development of the microscope and the telescope lead to increasing scientific knowledge? (p.224)

24. Extending Human Vision
Types of Telescopes:
1) Refracting: light from distant objects is collected and focused by a convex lens called the objective lens
Objective lens = Convex Lens
2)Reflecting: Uses a concave mirror to collect rays of light from distant objects. The concave mirror is called the objective mirror.
RECAP:
Refracting = Convex LENS (Objective LENS)
Reflecting = Concave MIRROR (Objective MIRROR)

25. Binoculars
Binoculars are two reflecting telescopes mounted side by side

26. Microscopes https://www.youtube.com/watch?v=Ue- 86MDmjns
Who was credited for the Microscope
Look at the figure of the microscope on page 224 – how many lenses are present?
How has the Microscope changed history?

27. Your Task
The questions in your notes.