Perception of Color – Bellwork If a student hiking through Black Canyon in Gunnison calls out and the echo is heard 1.20s later, how far away is the other canyon wall (at 32o C)?

Perception of Color – Bellwork When the student gets to Warner Point, he drops a rock and listens for the sound of it striking the bottom of the canyon. If the canyon is 2722 ft deep at this point, how much time will it take for him to hear the sound?

Bellwork 05/10/10 If a person could travel at the speed of light, it would take 4.3 years to reach the nearest star, Proxima Centauri. How far away, in meters, is Proxima Centauri (ignore relativistic effects). When you go out in the sun, it is the UV light that gives you your tan. The pigment in your skin called melanin is activated by the enzyme tyrosinase, which has been stimulated by UV light. What is the wavelength of this light if it has a frequency of 7.89 x 1014 Hz? When you are looking at a distant star or planet, you are looking back in time. How far back in time are you looking when you observe Pluto through the telescope from a distance of 5.91 x 1012 m?

Bellwork 05/13/09 The diagrams depict a sheet of paper being illuminated with white light (ROYGBIV). The papers are impregnated with a chemical capable of absorbing one or more of the colors of white light. In each case, determine which color(s) of light are reflected by the paper and what color the paper will appear to an observer.

Reflection, Absorption, and Transmission of Light If a light wave of a given frequency strikes a material with electrons having the same vibrational frequencies, then those electrons will absorb the energy of the light wave and transform it Into vibrational motion Reflection and transmission of light waves occur because the frequencies of the light waves do not match the natural frequencies of vibration of the objects.

Color Addition The production of various colors of light by the mixing of the three primary colors of light, Red, Green, and Blue Yellow, Magenta and Cyan secondary colors of light since they are produced by the addition of equal intensities of two primary colors of light. Any two colors of light which when mixed together in equal intensities produce white are said to be complementary colors

Two lights are arranged above a white sheet of paper Two lights are arranged above a white sheet of paper. When the lights are turned on they illuminate the entire sheet of paper (as seen in the diagram below). Each light bulb emits a primary color of light - red (R), green (G), and blue (B). Depending on which primary color of light is used, the paper will appear a different color. Express your understanding of color addition by determining the color which the sheet of paper will appear in the diagrams below

Color Subtraction The color appearance of an object is determined by beginning with a single color or mixture of colors and identifying which color or colors of light are subtracted from the original set Materials which have been permeated by specific pigments will selectively absorb specific frequencies of light in order to produce a desired appearance. Pigments absorb light. Pure pigments absorb a single frequency or color of light. The color of light absorbed by a pigment is merely the complementary color of that pigment.

1. Determine the color appearance of the same shirts if illuminated with other colors of light 2. Magenta light shines on a sheet of paper containing a yellow pigment. Determine the appearance of the paper. Practice A: Magenta light is a mixture of red light and blue light in equal intensities. Blue light must be subtracted since it is absorbed. When subtracting blue light from red and blue light, the red remains. The shirt appears red. (R + B) - B = R   Practice B: Red light is a primary color. Blue light would have to be subtracted if present. Since it is not present, there is no need to worry about it. Red light is reflected and the shirt appears red.   Practice C: Blue light is a primary color. Blue light must be subtracted since it is absorbed. There is no other color left to reflect to our eyes. The shirt appears black since black is the absence of reflected light. Magenta light can be thought of as consisting of red light and blue light. A yellow pigment is capable of absorbing blue light. Thus, blue is subtracted from the light which shines on the paper. This leaves red light. If the paper reflects the red light, then the paper will look red. M - B = (R + B) - B = R

Filters and Color Subtraction Transparent materials selectively absorb one or more frequencies of light and transmit what is not absorbed In Example A, white light (i.e., a mixture of red, green and blue) shines upon a magenta filter. Magenta absorbs its complementary color - green. Thus, green is subtracted from white light. That leaves red and blue light to be transmitted by the filter. For this reason, the filter will appear magenta (recall that magenta light is a mixture of red and blue light) when illuminated with white light. This process of color subtraction can be represented by the following equation. W - G = (R + G + B) - G = R + B = M In Example B, yellow light (i.e., a mixture of red and green) shines upon the same magenta filter. Magenta absorbs its complementary color - green. Thus, green is subtracted from yellow light. That leaves red light to be transmitted by the filter. For this reason, the filter will appear red when illuminated with yellow light. This process of color subtraction can be represented by the following equation. Y - G = (R + G) - G = R In Example C, cyan light (i.e., a mixture of blue and green) shines upon the same magenta filter. Magenta absorbs its complementary color - green. Thus, green is subtracted from cyan light. That leaves blue light to be transmitted by the filter. For this reason, the filter will appear blue when illuminated with cyan light. This process of color subtraction can be represented by the following equation. C - G = (B + G) - G = B

Primary Colors of Paint Magenta paints absorb green light. Cyan paints absorb red light. Yellow paints absorb blue light.

Blue jeans appear blue because the jeans are permeated by a chemical dye. Explain the role of the dye. That is, what does the dye do (absorb or reflect) to the various frequencies of white light? White light (red-green-blue) is shown incident on a sheet of paper which is painted with a pigment which absorbs one of the primary colors of light. For each diagram, determine the color of the two reflected rays and determine the color which the paper appears.

Reflection and the Ray Model of Light Light is said to have a wave-particle duality, causing it to behave as both an electromagnetic wave and as a particle, called a photon. Rays are used to describe the path of the photons of light as they are absorbed, reflected, or refracted. In the process of determining the image location, the manner in which light from the object travels to your eye is investigated. First, the method of parallax is used to locate the image of the object. Two pencils are inserted into rubber stoppers; one stoppered pencil serves as the object and the other serves to assist the student in locating the image. The object pencil is placed in front of a plane mirror. Then the student sights at the image of the object pencil in the mirror. As a student sights along a line (the line of sight) at the image of the pencil, the second pencil is placed behind the mirror along the same line of sight; this is called the image pencil. When placed along the line of sight, the portion of the image pencil which extends above the mirror will be aligned with the image that is seen in the mirror. Then the eye location is repositioned to the other side of the object pencil and the process is repeated. The precise image location of the object is the location where all lines of sight intersect regardless of where the eye is located.

Reflection in a Plane Mirror Incident ray - the light ray approaching the mirror. The incident ray intersects the mirror at the same location where your line of sight intersects the mirror The light ray then reflects off the mirror and travels to your eye this ray of light is known as the reflected ray. Object distance = Image distance As you sight at the image of an object in the mirror (whether it be a stoppered pencil or any object), light travels along your line of sight towards your eye. The object is being illuminated by light in the room; a countless number of rays of light are reflecting off the object in a variety of directions. When viewing the image of the object in a plane mirror, one of these rays of light originates at the object location and first travels along a line towards the mirror (as represented by the blue ray in the diagram below). This ray of light is known as the incident ray - the light ray approaching the mirror. The incident ray intersects the mirror at the same location where your line of sight intersects the mirror. The light ray then reflects off the mirror and travels to your eye (as represented by the red ray in the diagram below); this ray of light is known as the reflected ray.

Law of Reflection The angle between the incident ray and the normal is known as the angle of incidence. The angle between the reflected ray and the normal is known as the angle of reflection When a ray of light reflects off a surface, the angle of incidence is equal to the angle of reflection.

Consider the diagram below Consider the diagram below. Which one of the angles is the angle of incidence? Which one of the angles is the angle of reflection? A ray of light is incident towards a plane mirror at an angle of 30-degrees with the mirror surface. What will be the angle of reflection?

Spherical Mirrors

Refraction and the Ray Model of Light The transmitted wave undergoes refraction (or bending) Refraction occurs only at a boundary. Once the light has crossed the boundary between the two media, it continues to travel in a straight line.

Which Way Will Light Bend? FST = Fast to Slow, Towards Normal If a ray of light passes across the boundary from a material in which it travels fast into a material in which travels slower, then the light ray will bend towards the normal line. SFA = Slow to Fast, Away From Normal If a ray of light passes across the boundary from a material in which it travels slow into a material in which travels faster, then the light ray will bend away from the normal line.

In each diagram, draw the "missing" ray (either incident or refracted) in order to appropriately show that the direction of bending is towards or away from the normal.