Electromagnetic Waves and Light

Electromagnetic Waves and Light Chapters 12-

Electromagnetic Spectrum

Electromagnetic Spectrum • Read pages 360-365 • You will be responsible for understanding how we use each of the types of electromagnetic waves

Properties of Light • When light waves pass through different media, they are refracted • Through a prism, they are separated by the wavelength of light • Though a lens, they bend to focus the rays

Light waves • Electromagnetic • Need no medium to travel through • We see only what is in the visible spectrum • Retain properties of waves

Electromagnetic Waves • Electromagnetic waves are transverse waves caused by the interaction of electric and magnetic fields and they do NOT need a medium to travel, all classified by their wavelength • Light waves are electromagnetic waves • We can see only the portion of the spectrum called visible light

Waves Problems • Energy is inversely proportional to the wavelength of a wave. Which of the following would have the highest energy? A wave with a wavelength of ______ meters. • A) 5 • B) 10 • C) 15 • D) 20

C. Mixing Colors • Filter • transparent material that absorbs all light colors except the filter color View Java Applet on filters.

C. Mixing Colors • Pigment • colored material that absorbs and reflects different colors • Primary pigment colors • cyan, magenta, yellow • subtractive colors • combine to form black • EX: color ink cartridges

C. Mixing Colors Light Pigment When mixing pigments, the color of the mixture is the color of light that both pigments reflect.

Negative Afterimage - One set of cones gets tired, and the remaining cones produce an image in the complimentary color.

Primary Colors of Light • Primary colors of light = red, green, and blue • Secondary colors=yellow, cyan, and magenta

Color • Complementary colors = 2 colors of light that can be combined to make white light • Objects appear a certain color because they reflect that color light and absorb all the others

Polarization • Polarization is the production of light in a single plane of oscillation • The intensity of light as it passes through a secondary polarizing filter decreases

Holography • Holography= a technique that produces a hologram • Hologram= a complete three-dimensional photographic image of an object

Reflection • Reflection is the change in direction of a wave at an interface between two different media so that the wave returns into the medium from which it originated. • Law of reflection: the angle of reflection=the angle of incidence • θr=θi

Reflection • Specular reflection = when light hits a smooth surface the rays are reflected in parallel • Diffuse reflection = when light hits a surface that is rough (on the level of the wavelength of light) the light scatters

Reflection • Reflected rays of light that enter the eye appear to originate at a point behind the mirror • Virtual image= a type of image formed by diverging light rays • Always on the opposite side of the mirror from the object

Convex vs Concave

Concave Mirrors • If the object is outside the focal length, a concave mirror will form a real, inverted image.

Convex Mirrors • A convex mirror forms a virtual image.

Refraction • Refraction= the bending of light as it passes into a new medium • Snell’s Law of Refraction: • n1sinѲ1= n2sinѲ2 • n= index of refraction

Refraction • Index of Refraction= the ratio of the speed of light in a vacuum to the speed of light in that medium • The index of refraction determines how much the light bends/refracts • n=c/v

Total Internal Reflection • Phenomenon that occurs when light traveling from a region of a higher index of refraction to a region of lower index of refraction strikes the boundary at an angle greater than the critical angle such that all light reflects back into the region of higher index • Critical angle = the angle of incidence above which total internal reflection occurs

Total Internal Reflection

Holography • Holography is "lensless photography" in which an image is captured not as an image focused on film, but as an interference pattern at the film. • Typically, coherent light from a laser is reflected from an object and combined at the film with light from a reference beam. • This recorded interference pattern actually contains much more information that a focused image, and enables the viewer to view a true three-dimensional image

Interference and Diffraction Chapter 19

Interference • Incoherent light = light with unsynchronized wave fronts that illuminates objects with an even, white light • EX: the light you see when you look at objects illuminated by a light bulb • Coherent light= light from two or more sources that add together in superposition to produce smooth wave fronts

Interference • Interference fringes = a pattern of light and dark bands on a screen, resulting from the constructive and destructive interference of light waves passing through two narrow, closely spaced slits in a barrier

Interference • Thin-film interference : a phenomenon in which a spectrum of colors is produced die to the constructive and destructive interference of light waves reflected in a thin film

Diffraction • The phenomenon of diffraction involves the spreading out of waves past openings which are on the order of the wavelength of the wave • Diffraction pattern : a pattern on a screen of constructive and destructive interference of Huygens’ wavelets

Diffraction • Diffraction Grating = a device made up of many single slits that diffract light and form a diffraction pattern that is an overlap of single-slit diffraction patterns • The tracks of a compact disc act as a diffraction grating, producing a separation of the colors of white light.

Color Puzzles • WOOT!

Homework • You NEED to have read Chapters 10-14 • This covers everything that we have talked about with waves, sound, light, mirrors, and lenses • It would be a good idea to try some of the practice problems at the end of each chapter IN ADDITION to completing the review pages in the packet

Electromagnetic Waves and Light