Tuesday, September 7

Tuesday, September 7

Video links 1. http://www.youtube.com/watch?v=YK9BUQl9qxA (uk convex mirrors) 2. http://www.youtube.com/watch?v=zjCNKq_EN3c (2:18- 6:07) concave reflectors How Light Enters the Eye 1. Pupil: the black opening that lets light into

your eye. 2. Iris: the colored circle of muscle around the pupil that dilates (gets bigger) or contracts (gets smaller) to control the amount of light entering the eye.

3. Cornea: a tough, transparent tissue that holds your eye together and focuses light. Has no blood vessels. 4. Sclera: the opaque white tissue around

the cornea. 5. Retina: light sensitive tissue at the back of the eye, where light rays are focused and an image is formed.

6. Optic Nerve: a nerve that carries electrical signals from the eye to the brain. 7. Fluid: provide support by filling the spaces in the eye, supplies nutrients to the

cornea. 8. Lens: a flexible, convex structure that focuses light http://www.youtube.com/watch? v=gvozcv8pS3c http://www.youtube.com/watch?

v=0HzWmldLDHI&feature=related B. The Cornea-Lens-Retina System 1. Light rays are refracted by the cornea so that they converge toward the retina. A

convex lens behind the cornea fine-tunes the focus when muscles around it change its shape becoming thicker to focus on object close by, and becoming thinner to focus on objects far away.

2. The image that forms on the back of the eye is upside-down (inverted). 3. The area where the optic enters the retina does not have light-sensing cells, so it is called the blind spot.

http://www.youtube.com/watch? v=cFVbLnXWn6A C. Black and White and Colour Vision 1. Rod cells: black and white vision, and help us see shape and movement in low light. They are

long, cylindrical shaped cells that absorb all colours of light (especially green). 2. Cone cells: allow us to detect colour. We have three kinds of cone cells, containing red, blue, and green sensitive pigments so that we can see all the different colours of light.

1. Normal vision: the convex lens in your eye can change shape (thicker or thinner) in order to make light rays converge on the retina and produce a sharp image.

2. Near-sightedness: When people can see things close by but not far away, it is because the lens causes the light rays to make an image in front of the retina and the image will not be clear. A concave lens make the light rays diverge enough so that the image forms at the

right location. (Mrs. Bakker) 3. Far-sightedness: When people can see things far away but not close by, it is because the light rays form an image behind the eye. A convex lens can make

the image form correctly. (Mrs. Lockwood) 4. Astigmatism: When peoples corneas are distorted and irregular, images can focus on more than one point on the retina. This

can also be corrected with glasses, contacts, or surgery. e. Blindness 1. Most people who are blind can detect some light or have very limited vision (for

instance, they can only see the edge or the middle of a whole scene). 2. Can be the result of disease or malnutrition, as is common in the developing world

3. Snow blindness: painful, temporary partial or complete blindness caused by the glare of the sun on things like snow. The Inuit wore snow goggles to prevent this.

4. Night blindness: when it is difficult or impossible to see in dim light, usually because the rod cells dont work. Vitamin A Campaign: http://www.youtube.com/watch?

v=AADuvZMZ0qM 5. Colour blindness: the ability to see only in shades of grey. It occurs for about one person in every 40 000. Colour vision deficiency, when it is hard to distinguish between colours like red and

green, is quite common (8% of males and 1% of females). Mantis Shrimp http://www.nature.com/news/mantisshrimp-s-super-colour-vision-debunked1.14578

Color Memory Video https://www.youtube.com/watch?v=0cpjh3iVjg

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