Ch. 18 Light

1. Ch. 18 Light

2. 18.1 Light and Color

3. Light in different materials • Light hitting an object is reflected, transmitted, or absorbed • Transparent Material: transmits most light without scattering; clearly see-through • Color of object is color of light transmitted • Translucent Material: scatters light; blurrily see-through • Color of object is color of light transmitted • OpaqueMaterial: reflects or absorbs all light; not see-through at all • Color of object is color of light reflected

4. Combining COlors • Primary Colors: three colors that combine to make any other color; all three together make white light • For light: red, green, blue • For pigment: magenta, yellow, cyan • Secondary Colors: equal combination of two primary colors • For light: magenta, yellow, cyan • For pigment: red, green, blue • Complimentary Colors: two colors that combine to form white light or black pigment

5. Combining colors • Pigment: colored substances that are used to color other materials • Absorb some colors and reflect others • As colors are added together, fewer color of light are reflected • Primary colors: cyan, yellow, magenta • All three create black • CYMK printers: four colors

6. 18.2 Reflection and mirrors

7. Reflection of light rays • Rays: representation of light waves as straight lines • Regular Reflection: parallel light rays hit a smooth surface, reflect at same angle, and form a sharp reflection • Diffuse Reflection: parallel light rays hit an uneven surface, reflect at different angles, and form a blurry reflection

8. Plane Mirrors • Plane mirror: sheet of glass with smooth, silver coating on back which reflects light (regularly) • Creates an upright virtual image the same size as actual object, but left and right sides are reversed • Image: copy of an object formed by reflected or refracted light rays • Virtual Image: upright image that forms where light seems to come from

9. Virtual Image

10. Concave Mirrors • Concave Mirror: mirror with surface that curves inward • Form virtual or real images (depending on shape of mirror) • Optical Axis: imaginary line that divides mirror in half • Focal Point: point at which rays parallel to optical axis meet • Location depends on shape of mirror • More curved mirrors have focal point closer to the mirror • Real Image: forms when rays actually meet; upside down; may be smaller or larger than actual object

11. Convex Mirrors • Convex Mirrors: mirror with a surface that curves outward • Rays never meet; appear to come from focal point behind the mirror • Image is always virtual and smaller than actual object

12. 18.3 Refraction and lenses

13. Refraction of Light • Refraction: when light rays enter a medium at an angle, the change in speed causes light to bend • Index of Refraction: a measure of how much light rays bend when entering that specific material • Water= 1.33 • Glass = 1.5 • Glass bends light more than water • Mirage: image of a distant object caused by refraction of light

14. lenses • Lens: a curved piece of glass or transparent material used to refract light • Convex lens: thicker in center than edges • Bends light toward the center of the lens • Object’s position relative to focal point determines whether real or virtual image is formed

15. lenses • Concave lens: thinner in center than edges • Bends light away from center of the lens • Only virtual images produced

16. 18.4 Seeing Light

17. The human eye • Cornea: transparent surface through which light enters the eye • Pupil: opening through which light enters the inside of the eye • Iris: ring of muscle that changes the size of the pupil • Convex lens forms an image on the lining of the eyeball • Retina: layer of cells that lines the inside of the eyeball; made of rods and cones

18. The human eye • Rods: cells that contain a pigment that responds to small amounts of light • Cones: cells that respond to color (red, green, or blue light); respond best in bright light • Optic nerve: takes signals from rods and cones to the brain • Brain: interprets signals as upright images and combines images from each eye to create a 3D image

21. Correcting vision • Nearsighted: can see nearby things clearly • Corrected with concave lenses • Farsighted: can see distant things clearly • Corrected with convex lenses

22. 18.5 Using Light

23. Optical instruments • Telescope: forms enlarged images of distant objects by using lenses or mirrors to collect and focus light • Refracting Telescope: uses two convex lenses; images are upside-down • Objective lens: larger lens that gathers light coming from an object and focuses rays to form a real image • Eyepiece: closer lens, magnifies the image to see clearly • Reflecting Telescope: uses a concave mirror to collect light and form a real image; small mirror reflects the image to the eyepiece; image seen upside-down • Microscope: forms enlarged images of tiny objects using a combination of convex lenses • Camera: uses lens(es) to focus light and film (or sensor) to record an image

24. Lasers • Laser: produces a beam of coherent light (all same wavelength, crests align with each other); from the phrase light amplification by stimulated emission of radiation • Uses of lasers: • Read information on CDs • Holograms: 3D photographs created by laser etching • Laser surgery: eye restructuring or removing cancers

25. Optical Fibers • Optical fibers: long, thin strands of glass or plastic that carry light for long distances • Total internal reflection: light is completely reflected by the inside surface of a medium; occurs when angle of incidence is great enough • Uses: • Medicine: optical fibers can be inserted to scope out areas or illuminate surgery • Communications: electrical signals are changed into pulses of light by tiny lasers and sent long distances through optical fibers; stronger and faster signals than in copper wires