2. Physics Mrs. Tobler

3. What is Light? Debated by scientists –Dual “Personality” Acts like transverse waves Acts like it is made of particles –Photons (packets of energy) Light is a form of energy

4. Light as a Wave Light travels as a transverse wave –Made up of Electric and Magnetic Fields moving perpendicular to one another Light is a range of frequencies of electromagnetic waves –A.K.A. Electromagnetic Radiation

5. Properties of Electromagnetic Waves Travel at 3.0 x 10 8 m/s in a vacuum (empty space) Light year = distance light travels in one year (about 6 trillion miles) –The light from a star 4 light years away traveled for 4 years before reaching your eyes –Light from our own sun takes 8 minutes to reach Earth –When you look at the stars you are looking into the past Transmit energy via Radiation –Don’t need a medium Slow down when it enters a medium. –Diamond slows it down to 124 m/sDiamond slows it down to 124 m/s

7. Visible Light Remember “ROY G BIV” Which has a longer wavelength Orange or Blue? –Orange

8. Complete the Spectrum

9. Uses for Electromagnetic Waves Radio Waves –Transmit TV, AM & FM –Satellite radio –Cell phones –RADAR for communication and police Microwaves –Cook food by exciting water molecules to produce heat

10. Infrared –Keep food warm (like at McDonald’s or Luby’s) –Night vision Ultraviolet –Suntans, skin cancer –Sterilize goggles and other items –Fluorescence (Black Light) X-rays –For looking at bones such as teeth or broken arm Gamma –To kill off cancer cells –Can also damage healthy cells Uses Continued

11. Why can’t we see all electromagnetic waves? Human eyes contain rods and cones in the retina that are sensitive to only a small range of frequencies We see only reflected or emitted light –Reflected = waves bounce off of a surface back to our eyes –Emitted = object produces light at frequencies our eyes can detect

12. What color is white light? Isaac Newton –Discovered white light consists of various colors of light in 1666 using prisms Made of the 3 Primary Colors of LightPrimary Colors of Light –Red –Blue –Green

13. How we See Color Our eyes detect the color (frequency) of light that is being Reflected off of a surface. Reflected –If an object appears blue that means blue light is bouncing off of the object and the other colors of light are absorbed What happens to the light if the object appears white? What if it appears black?

14. More Fun with Color Primary colors of Pigments Magenta Cyan Yellow –Color printers use these same colors Color Filters –If an object reflects red light when exposed to white light, then when exposed to green light the object will appear almost black because there is NO red light to reflect.

15. Behaviors of Light All electromagnetic waves experience the following wave behaviors similar to mechanical waves –Reflection –Refraction –Diffraction –Interference Constructive Destructive –Polarization

16. Words to Know Ray = beam of electromagnetic radiation (light) Normal = imaginary line that is perpendicular to the surface of an object Incident Ray = emitted or incoming light ray Reflected Ray = light ray that bounces off a surface; outgoing wave Angle of Incidence = angle at which the incoming light ray hits a surface Angle of Reflection = angle at which reflected light ray leaves the surface

17. Reflection of Light Occurs when a wave reaches a boundary between 2 different mediums which causes –The wave to bounce back into the 1st medium (totally reflected) –Or some of the wave bounces back and some is absorbed into the 2nd boundary (partially reflected). Depends on how rigid the boundary is –Very rigid then most of the wave is reflected –Less rigid then only some of the wave is reflected

18. Law of Reflection When a wave hits a boundary the angle of incidence equals the angle of reflection. –Also true when playing wall ball, basketball and tennis

19. Complete the Reflection Diagram

20. Diffraction Bending of a wave around a barrier, such as an obstacle or the edges of an opening. –Amount depends on the size of the wavelength compared with the size of the obstruction or opening. Wide opening = less bending Narrow openings = more bending Thomas Young’s Double Slit ExperimentThomas Young’s Double Slit Experiment

21. Diffraction Gratings A series of closely spaced parallel slits or grooves Used to separate colors of light by interference. –Used instead of a prism –Found in objects used to reflect various colors of light Back of CDs & DVDs Bird feathers

23. Total internal Reflection At a certain angle (critical angle)— no ray will emerge into the air above the surface. –For water it is 48  which does not allow the ray to enter the air, it is only reflected inside the water. –Other Examples Glass (43  ) Mirrors (90-95  ) Diamonds (24.6  )

24. Review Refraction Bending of a wave as it enters a new medium due to a change in velocity. –Angle of Incidence is NOT EQUAL to the Angle of Refraction Refraction of Sound Even though speed of sound is greater in warm air; sound waves bend away from the ground which doesn’t allow it to carry as well. In cold air sound bends toward the ground and sound carries well.

25. Refraction of Light Less dense to More dense medium –Speed of light slows down –Refracted Ray bends toward the normal air to glass More dense to Less dense medium –Speed increases –Ray bends away from the normal. water to air As it leaves the new medium it goes back to the original angle.

26. Complete the Refraction Diagram

27. Observing objects in Water

28. Refraction of Light Causes white light to separate into the primary colors as it passes through the water droplets

29. How are Rainbows Produced? Water droplets act like prisms Each color of light is refracted at a different angle due to its frequency –Violet has the highest frequency and is refracted the most. –Red has the lowest frequency and is refracted the least. Sun has to be behind the observer Circular rainbows can be seen from airplanes

30. Atmospheric Refraction Mirage – caused by change in air temperature resulting in light refraction –Road appears to be wet Actually reflection of the sky

31. Why is the Sky Blue? Light from the sun gets scattered as it collides/passes through molecules in the atmosphere –Blue light is scattered the most because of its short wavelength

32. Index of Refraction Unique to the substance –Based on density Ratio between the speed of light in a vacuum to the speed in a particular material n = index of refraction c = speed of light in vacuum (3x10 8 m/s) v = velocity of light in material

33. Example Index of Refractions MaterialRefractive Index Air1.0003 Water1.333 Glycerin1.473 Immersion Oil1.515 Crown Glass1.520 Flint Glass1.656 Zircon1.920 Diamond2.417 Lead Sulfide3.910

34. Polarization of Light The aligning of vibrations in an electromagnetic wave, usually by filtering out waves of other directions. Polarized Filter –Only allows waves through that are parallel to the slits Occurs only with transverse waves –Not all light is polarized

35. How Polarization Works

36. Fiber Optics A.K.A. Optical fibers or light pipes Thin glass fibers –Use total internal reflection Developed for communication and data transmission –Replacing electric circuits and microwave links Thousands of miles of it in our phone lines

38. Polarized Sunglasses. Only allow light that is in the same direction as its polarized axis to pass. –If polarization axis of 2 filters are at right angles to each other then the light can’t pass through.

39. Traditional 3-D Glasses The red and blue lenses filter the two projected images allowing only one image to enter each eye. Brain combines to images to look 3-D

40. Modern 3-D Glasses Uses polarized filters instead of color Allow only one of the images into each eye because each lens has a different polarization.