Check & Reflect Answers p. 208 2. 3. There is no image formed when the object is placed at the focal point of a convex lens 4. The glass in the building bricks is curvy and wavy, consisting of irregular convex and concave surfaces. Light that travels through these bricks and is bent in unpredictable directions. This means that clear images cannot be formed. And so people outside can’t see a clear image of what’s inside.

Image Formation in Eyes and Cameras Copy This Down Image Formation in Eyes and Cameras 4.1

Copy This Down How Light Gets In Both eyes (natural) and cameras (artificial) are image producing technologies. A camera is very similar to how an eye works        

Anatomy of an Eye and a Camera Aperture Lens Film Diaphragm

Similarities between an eye and a camera: Human Eye Camera How does light enter? Pupil Aperture What controls the amount of light? Iris Diaphragm What interprets the image? Retina Film How is the light focused? Lens

Comparing the Eye and the Camera Copy This Down Comparing the Eye and the Camera There are many similarities between the human eye and the camera.  

Copy This Down Eye Anatomy - The pupil is the opening; the amount of light that enters is controlled by the iris. - The iris is made up of a circular band of muscles.                                                 

Iris Controlling the Light Copy This Down Iris Controlling the Light In bright light the iris constricts, becoming smaller, and reduces the light. -In dim light the iris dilates, becoming larger, and increases the light.

When Light Gets Inside… Copy This Down When Light Gets Inside… - To see, the light must hit the sensitive retina at the back of the eye, which has 2 types of light sensitive photoreceptors. 1)      Rods - highly sensitive to small amounts of light (dim light). allows for seeing in the dark (when there is enough light reflected!!) more rods on the outside of the retina 2)      Cones - sensitive to bright lights, and they detect colour. - almost exclusive in the retina

Rods & Cones When photoreceptors are stimulated they send a message to the optic nerve, which then sends the message to the brain, where it is translated and interpreted.

Copy This Down More about Rods & cones - Cones can’t function in low light, so we only see shades of gray in low light because only rods are stimulated -

Just For Fun…P.233 .                                                                                

Copy This Down Focusing the Light In order to form a clear & sharp image the focal point must land on the retina. o       In the eye there are muscles that control the shape of the lens.

Images Produced In a camera the lens is moved forward and backward. Copy This Down Images Produced In a camera the lens is moved forward and backward. The upside-down image produced by the lens is not a problem because the brain interprets the world right side up, and film can be developed either way.

Correcting Vision Problems with Lenses Copy This Down Correcting Vision Problems with Lenses Nearsightedness –can see near, but cannot see far. the eye cannot make the lens thin enough to focus the light on the retina, so a concave lens is used to converge the light onto the retina.

Correcting Vision Problems with Lenses Copy This Down Correcting Vision Problems with Lenses Farsightedness - can see far, but cannot see near. the eye cannot make the lens fat enough to focus light on the retina, so a convex lens is used to diverge the light onto the lens.

Fixing other vision problems Laser Eye Surgery the lens is reshaped by a laser (helps focus light). Night Vision Goggles - the low light is intensified by phosphor-coated screen (looks green).

Eye Spy The lens in the human eye is a convex lens, which focuses the light rays entering your eye to a point on your retina (a light sensitive area at the back of the eye).  The image you see is formed on the retina.  Some people however have eyes that are too long or too short.   If their eye is too long, the image forms in front of the retina - this is a condition called Myopic, or near-sightedness   (they have trouble seeing distant objects).   If their eye is too short, the image forms behind the retina, making object that are close to them difficult to see.  This condition is called far-sightedness.

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Homework! Check & Reflect p. 235 1 2