1. Chapter 19 Light

2. 19 – 1 Electromagnetic Radiation Electromagnetic spectrum – energy waves that include: radio waves, microwaves, infrared, visible light, ultraviolet, x-rays, and gamma rays. They are transverse rays. See Figure 19-2 p.485 –Electromagnetic waves carry energy by radiation – they can travel through a medium and through a vacuum (space). –All electromagnetic waves travel at 300,000 km/sec or 186,000 miles/sec. This is the speed of light (c) it is also the speed of any of these waves in a vacuum or medium. –Light is composed of tiny particles of radiation called photons – they have no mass.

5. 19 – 1 Electromagnetic Radiation Radio waves – long wavelengths, low frequency, lowest photon energy. –Radio waves are used to transmit sound waves – these machines change sound waves to electrical currents through modulation. The machines then change the electrical currents back to sound waves. –Radio waves include microwaves (used in communications), AM & FM radio, radar, shortwave radio, television.

6. 19 – 1 Electromagnetic Radiation Infrared waves – longer wavelengths than visible light, infrared is warm: warm objects give off more infrared radiation than cool objects. “Night vision” goggles use the infrared radiation of animals to “see” animals. Medical diagnosis use infrared to detect tumors; infrared lamps are used to keep food warm and to dry paint. (p. 487) Visible light – only a small portion of the electro-magnetic spectrum is visible. Light can stimulate chemical reactions (photosynthesis). (see chart pg 485)

8. 19 – 1 Electromagnetic Radiation UV radiation – higher frequency, shorter wavelengths, than visible light. Their energy is greater than visible light. Because this energy is greater, overexposure can cause cancer. The ozone layer is a natural filter. However, we do need some UV in order to produce vitamin D for bones and teeth. UV radiation is also used to kill bacteria and microbes in foods and on utensils.

9. 19 – 1 Electromagnetic Radiation X – rays: x-rays have shorter wavelengths, higher frequencies than UV. They can travel through less dense skin & muscle but not through bone so they form an image. Gamma rays  : have the highest frequency and the lowest / shorter wavelength; radioactive; used to treat cancer.

11. 19 – 2 Light & Color Light rays pass through objects at different values. A color “appears” because of the light rays the object reflects. ( EX: a green shirt reflects green rays, absorbs all other ). The type of matter in an object determines the amount of light absorbed or reflected. –Opaque – absorb or reflect all light so you can’t see through the substance. –Transparent – light rays pass through so you can see through (most glass) –Translucent – some light passes through but you can’t see clearly (wax paper, frosted glass, white paper)

12. 19 – 2 Light & Color Objects appear a particular color because of the reflected rays. Black absorbs all light (so it gets hot) white reflects all rays (so it is cooler). –Rods and cones are the nerve cells in the eye that allow us to see colors – rods allow us to see in dim light, cones allow us to see colors.

13. 19 – 2 Light & Color The wavelength of visible light gets shorter across the spectrum: Red (longest ), Orange, Yellow, Green, Blue, Indigo, Violet (shortest ). ROYGBIV (the colors of the rainbow)

16. 19 – 2 Light & Color –Filters can be used on bright lights (spotlights) to change colors. It will transmit only that color. A pink filter will make everything look pink (or black/grey if it is not pink or red) because it reflects that one color wavelength and absorbs all other wavelengths.

17. 19 – 2 Light & Color Pigments – materials and chemicals that absorb some colors & reflect others. Pigments are “opposite” of cones: yellow pigments reflect red & green light waves and absorb blue. (p. 495) Light rays are additive because they combine & produce white light. Pigments are subtractive because they combine to produce black and black is the absence of color.

18. 19 – 3 Battle of the Bulbs Incandescent Light – produced by electricity passing through/across a tungsten filament, causing the filament to heat up and glow. The bulb is hot to the touch. Fluorescent Lights are filled with a gas and coated on the inside of the glass tube with phosphers (fluorescent materials that give off light when they absorb UV radiation). Electricity passes through the tube, collide with the gas molecules causing them to give off UV radiation which is absorbed by the phosphors, causing them to glow.

22. 19 – 3 Battle of the Bulbs Fluorescent lights are much less expensive to use than incandescent. For each bulb replaced in the home, about $20 per bulb can be saved yearly on electric bills. Also, the use of fossil fuels would decrease creating less pollution.

23. 19 – 4 Wave properties of Light Reflection occurs when light waves/rays strike an object and “bounces off”. Light and electromagnetic waves, sound and water waves can all be reflected.

24. 19 – 4 Reflection –Law of reflection – angle of incidence (i) equals angle of reflection (r) smooth surface – Smooth surfaces reflect light waves in one direction; rough surfaces scatter waves.

25. 19 – 4 Wave properties of Light Refraction – the “bending” of light waves caused by a change in speed. The light waves change speed when they pass through a substance with a different density. Diffraction – the bending of waves around corners or a barrier.

26. 19 – 4 Refraction –Normal – the line perpendicular to the surface the light is moving into –Angle of incidence ( i ) – angle between the normal and the surface the wave is entering. –Angle of refraction ( r’ ) – angle between normal and inside the entered medium. –Example: see Figure 19-17 p.502

27. 19 – 4 Refraction –When light passes into a more dense substance, it travels slower so it bends toward the normal. –When light passes into a less dense substance, it travels faster and bends away from the normal. –When light passes through a prism it bends, and a rainbow is formed. R O Y G B I V –Diffraction grating is a piece of glass or plastic made up of many parallel slits that can separate white light.