Light

Light When light strikes an object, it can be reflected, absorbed, or transmitted.

Opaque objects reflect or absorb all the light that strike it. (exm Opaque objects reflect or absorb all the light that strike it. (exm. wood, metal, and cotton/wool fabrics) Transparent materials transmit light, this means light passes right through it allowing you to see what’s on the other side. (exm. clear glass, water, air) Translucent materials allow some light to pass through however it does not allow you to see details clearly. (exm. frosted glass, wax paper)

Reflection You can see most objects because light reflects, or bounces, off them. What you see when you look at an object depends on how it’s surface reflects lights. Mirrors for example, allows light to pass through the glass, but the coating on the back reflects light allowing you to see an image.

Color Objects appear a certain color depending on the color of light it reflects (exm. red apples reflect red light, green apples reflect green light) White reflects all light Black absorbs all light

Refraction Light can also cause refraction, this occurs when rays enter a new medium at an angle causing them to bend or change direction. This can cause you to see things that aren’t there (mirages) It can also cause you to see rainbows. When sun shines through tiny droplets of water, the droplets act like prisms refracting, reflecting and separating the colors.

Cornea and Pupil The eye is the organ of sight Light enters the eye through the transparent front surface called the cornea. It acts as a lens bending rays of light as they enter the eye. The pupil is the dark hole in your eye, it gets larger in dim light and smaller in bright light to reduce the amount of light that enters the eye.

Lens Behind the pupil is the lens, the lens refracts light forming an image on the lining of your eyeball The ciliary muscles holding the lens in place contract when you focus on distant objects. They relax when you focus on a nearby object.

Retina Inside the eyeball, is the retina. The retina is the layer of cells lining the inside of they eyeball. As the cornea and lens refract light, an upside- down image is formed on the retina. The cells that make up the retina are rods and cones. Rods respond to small amounts of light, they are important for night vision. Cones respond to color, they only function in bright light. The different types of cones detect green light, red light, and blue light.

Optic Nerve The signals generated by the rods and cones travel through your brain through a short, thick nerve called the optic nerve. When the signals reach the brain, it automatically turns the images right-side up.

Corrective Lenses In some people, the eyeball is slightly too long or too short so the image in the retina is out of focus. Glasses and contacts lenses usually correct this type of vision problem. The lenses in eyeglasses can be convex or concave.

Nearsightedness Nearsightedness- means a person can see nearby things clearly, but objects at a distance appear blurry. This happens because the eyeball is a little too long. Concave lenses can be used to correct this problem by spreading out the rays a little before they enter the lens of the eye.

Farsightedness Farsightedness- means a person can see distant objects, but nearby objects are blurry. This happens when the eyeball is a little too short. Convex lenses can correct this issue by making the rays bend toward each other a little before they enter the eye.