ch14_bkes

=Chapter 14 - Light and Reflection =  **//__14.1 Characteristics of Light __//** Electromagnetic wave: a transverse wave consisting of oscillating elecric and magnetic fields at right angles to each other. The Electromagnetic Spectrum (classification of all types of electromagnetic waves) and their applications are as follows:


 * Radio Waves (AM and FM radio, TV)
 * Microwaves (radar; aircraft navigation; microwaves
 * Infrared Waves (infrared photography; physical therapy)
 * Visible Light (photography; optical microscopy; astronomy)
 * Ultraviolet Light (sterilization of medial instruments; identification of fluorescent minerals)
 * X-Rays (medical examinations of bones, teeth, vital organs; treatment for cancer)
 * Gamma Rays (examination of thick materials for structural flaws, cancer treatment, food irradiation)

Because all electromagnetic waves move at the speed of light, it is worth knowing the equation for Wave Speed and the constant for the speed of light: math \displaystyle c = f \lambda math

when math \displaystyle c = 3.00 x 10^8 m/s math

Waves can also be approximated as rays. All the points on the wave front of a plane wave can be treated as point sources. Each one of these points produces a circular/spherical secondary wave, called a //wavelet.// This phenomenon can be described by Huygens' Principle. It derives properties of waves that interact with matter and says that the same results can be obtained by treating the wave as a straight line perpendicular to the wave front.

Brightness of these light waves decreases by the square of the distance from the source. Simply put, the further away from a light source an object is, the dimmer it will be.

__Section Review__ 1. What kind of electromagnetic waves does the microwave oven use? 2. If an electromagnetic wave has a frequency of 7.17 x 10^14 Hz, what is the wavelength? 3. If you are 3 m from a light source, how much brighter/dimmer will the light seem?

//Answers: 1: Microwaves. 2: 4.18 x 10^-7 m 3: 1/9 the brightness or 9 times dimmer.//

__ //**14.2 Flat Mirrors**// __ Reflection of Light ** //Reflection// is the change in the direction of light. The texture of the reflecting surface affects how light will be reflected. When you have a rough surface, the reflection is called //diffuse reflection.// With a smooth or shiny surface, the reflection you get is called //specular reflection.//

Incoming and reflected angles of the light beams are the same. In scientific terms, the **angle of incidence** always equals the **angle of reflection.** Relatively, math \displaystyle \theta = \theta' math

The simplest form of a mirror is a flat one. If an object is placed at some distance in front of a flat mirror, light bounces off the object, spreads out and reflects from the mirror's surface. These rays always appear to come from a location on the other side of the mirror. For that reason, the image is said to be behind the mirror. Because the rays never really come to a real point behind the mirror, it is called a **virtual image**. The //object distance, p,// will always be the smae as the //image distance, q.// The image formed by a flat mirror appears to have a right-to-left side reversal. This ray diagram will help.
 * Flat Mirrors**



__Section Review__: 1. Which is would produce a specular reflection: still water, concrete, or asphault? 2.Why does a flat mirror appear to reverse images right to left, but not up and down? 3. What is the sign for image distance? Object distance?

//Answers: 1. Still water 2. see ray diagram 3. q. p.//

**//__14.3 Curved Mirrors__//**

A spherical mirror with light reflecting from its silvered and concave surface can be called a **concave spherical mirror**. One factor that determines the shape and size of the image is the radius of curvature, //R.// The radius of curvature is the same as the radius of the spherical shell of the mirrors, so //R// can be called the distance from the mirror's surface to the center of curvature, //C.//
 * Concave Spherical Mirrors**

The location of the object/image can be predicted with the mirror equation.

Not only can you predict the location, you can also measure the //magnification// of the image. The magnification is the meaure of how large or small the image is with respect to the original object's size. We will use //M// for magnification. For an image in front of the mirror, //M// will be negative and the image will be //inverted (virtual).// When the image is "behind" the mirror, //m// is positive and the image is //upright (real).//

Ray diagrams are very helpful for curved mirrors. There will always be 3 light rays shown: The intersection of these lines will form the image.
 * 1) In parallel to Principal axis, out through the focal point.
 * 2) <span style="font-family: Georgia, serif;">In through the focal point, out through the Principal axis.
 * 3) <span style="font-family: Georgia, serif;">In through the center of curvature, out the same way.

A convex spherical mirror is a segment of a sphere that is silvered so that light is reflected from the sphere's outer, convex surface. It is also known as a diverging mirror because the rays diverge after reflection. Thus, the resulting image is always virtual. For the ray diagram, the same rays apply, but are drawn slightly differently: Note how the focal point and center of curvature are both behind the mirror.
 * Convex Spherical Mirrors **

The only true difference between parabolic and spherical mirrors is that parqabolic mirrors will eliminate the effects of //spherical aberration.// //Spherical aberration// happens when the reflected rays converge at a slightly different points on the principal axis. The diagram on the left shows a spherical mirror with spherical abberation. Conversely, the diagram on the right shows the parabolic mirror with no spherical abberation.
 * Parabolic Mirrors **

__ Section Review __ 1. A convex mirror with a focal length of 3 cm forms an image that has been placed 1.1 cm away from the mirror. Determine the image distance and magnification. It the image virtual or real? Inverted or upright? 2. Determine the image type: Shop aisles in a convex obvservation mirror; your beautiful face in a flat mirror. 3. What is the magnification of a pencil with an image distance of -3 cm and an object distance of 9 cm?

//Answers:// 1. //-1.7 cm. Virtual upright.// 2. //virtual upright, virtual upright.// 3. 1/3

__**A helpful chart:

// 14.4 Color and Polarization //**__

//__Additive primary colors__// produce white light when they are combined. Because white light can be dispersed into its elementary colors, we can suppose that elementary colors can be combined to form white light. This theory is demonstrated through this diagram:

//__Subtractive primary colors__// filter out all light when combined. When pigments are mixed, every one subtracts certain colors from white. The primary pigments are cyan, magenta, and yellow and they are the same colors that are complementary to the additive primary colors in the diagram above. When the 3 pigments are mixed all together, all the colors are subtracted from white and the mixture is black.

Light can be polarized linearly through transmission. This effect is similar to waving a rope through a picket fence. Only certain wave types will fit through the cracks.
 * //Polarization of Light Waves//**

Figure 14.22 shows the unpolarized whereas figure 14.23 shows polarized light.



Figure 14.24 demonstrates the picket-fence theory and the transverse rope wave.

//**Light can be polarized by reflection and scattering**// When light is reflected at a certain angle from a surface, the reflected light is completely polarized parallel to the reflecting surface. If the surface is parallel to the ground, the light is polarized horizontally; conversely, if the surface is perpendicular to the ground, it polarizes vertically.

Most glare-causing light can be horizontally polarized. Polarized sunglasses demonstrate this principle quite well. The unpolarized sunlight strikes polarizers with a vertical orientation and it blocks harmful rays from the sun, as demonstrated in Figure 14.26

Figure 14.27 demonstrates the idea that air molecules scatter polarized light because the electrons in the molecules begin vibrating with the electric field of the sun waves

Note: General format and pictures came from Mr. Strong's in class notes and Holt Rinehart Physics Textbook.