Light and Optics Week 3/4 Ms Deanne Science 8

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)

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.

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

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

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

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

Eye Spy

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

Evolution of the eye https://www.youtube.com/watch?v=qrKZBh8 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?

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 http://www.edumedia- sciences.com/en/media/6-the-eye http://www.edumedia- sciences.com/en/media/79-how-does-vision- work

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

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

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

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

Think about it! So why do people need glasses? https://youtu.be/ypF037wlYZg

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

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

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

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?

Pinhole Camera Flip to the assignment page in your booklet!

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)

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)

Binoculars Binoculars are two reflecting telescopes mounted side by side

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?

Your Task The questions in your notes.