PHYSICS InClass by SSL Technologies with S. Lancione Exercise-46 High School InClass by SSL Technologies with S. Lancione Exercise-46 Intro to Optics Part 2 /2

Intro to Optics PART-2 /2 In studying optics, it is convenient to classify objects into those that emit light (luminous) and those that reflect light (non-luminous): LUMINOUS (originate light) NON-LUMINOUS or ILLUMINATED (do not originate light) Incandescent Opaque (light cannot pass through) Neon Transparent (light and images pass through) Fluorescent Translucent (light passes through, images do not) BEAM OF LIGHT: A beam of light is a "bunch" of light rays. CONVERGENCE: When rays of light come together to meet at a point, they are said to converge. DIVERGENCE: When rays of light go away from a point, they are said to diverge. MEDIUM: A medium is the material through which light travels. Optical mediums are classified according to density. The more "optically dense" a material is, the slower light travels in that medium. Click

Intro to Optics THE PRIMARY COLORS Monochromatic light is light of one color. Polychromatic light is light of many colors. In everyday language we use names to represent monochromatic light such as red, orange, yellow, green, blue and violet. Furthermore, each of these colors has a variety of different shades. Collectively, all the different colors form the “light band” which is part of the “electromagnetic spectrum”. Click

Intro to Optics Red, green and blue light (RGB) are called the primary colors. Adding these three primary colors together forms “white” light. Adding pairs of the primary colors form the secondary colors. Click

Intro to Optics The color of an object is determined by the color (or colors) it reflects. Suppose white light shines on a red object. The object will absorb all the colors except red. Thus, it is red. Study the illustration below. Click

COLOR THEORY Inks Lights Additive color theory Subtractive color theory Primary colors: RGB Primary colors: CMY Red – Green – Blue Cyan – Magenta – Yellow Inks Lights Cyan = Green + Blue Red = Magenta + Yellow Magenta = Red + Blue Green = Cyan + Yellow Yellow = Red + Green Blue = Cyan + Magenta White = Red + Green + Blue Black = Cyan + Magenta + Yellow Click

Intro to Optics Penumbra (grey) Umbra (black) SHADOWS Shadows are formed when light is obstructed. The light may be totally obstructed thereby forming a dark shadow known as an umbra, or it may be partially obstructed thereby forming a gray shadow known as a penumbra. Penumbra (grey) Umbra (black) Click

Intro to Optics Click From the side view, we have two rays For example, in diagram-A below, a point source of light encounters an obstacle (a disc) causing an umbra (total darkness). In diagram-B, a large source of light causes both an umbra and a penumbra. Note that when the source is a point, the shadow consists of an umbra (total darkness) with a well defined outline. From the side view, we have two rays (one to the top of the obstruction, one to the bottom of the obstruction) to define the shadow (the light source has no top and bottom portions). Click

EXERCISES

Question-1 Define the following terms: a) Beam of light A stream of photons emanating (coming from) a light source. b) Medium The material through which light travels. c) Opaque A material that blocks light (light cannot pass through). d) Transparent A material through which light and images pass through. e) Translucent A material through which light can pass through but images cannot pass through. Click Click Click Click Click Click

Question-2 Define the meaning of the terms monochromatic and polychromatic light. Monochromatic is light consisting of only a single color. Polychromatic is light consisting of many colors. Click Click Click

Question-3 Draw 5 rays of light that are parallel, converging and diverging. Click Click

Question-4 What does RGB stand for? Red, Green and Blue. Click Click

Question-5 Fill in the primary and secondary colors in the chart below: Red Green Blue Yellow Cyan Magenta Click Click

Question-6 Define an umbra and explain how it is formed. The umbra consists of total darkness and is caused by the total obstruction of the light rays. Click Click

Question-7 Define an penumbra and explain how it is formed. The penumbra consists of partial darkness and is caused by the partial obstruction of light rays. Click Click

Question-8 In your own words, define light intensity. Light intensity (also known as brilliance) refers to the total number of photons emitted by a light source per second. Click Click

Question-9 Sketch the electromagnetic spectrum and indicate the position of light. Click Click

Question-10 In the given diagram, measure the length of the umbra and penumbra of the shadow formed by the obstruction (line). Click Click

Question-11 By definition A beam of white light strikes a glass prism producing an array of different colors as illustrated below. What optical phenomena does this represent? A) Specular reflection B) Total internal reflection C) Diffusion D) Dispersion By definition Click Click

Question-12 The diagram below illustrates light coming from the sun to the earth with the moon in between. Which of the following statements correctly describes the shadow of the moon on the earth? I- Region Y is the penumbra II- Regions X and Z are the umbra III- Regions Y is the umbra IV- Regions X and Z are the penumbra A) I and II B) I and IV C) II and III D) III and IV Click

Question-13 The diagram below illustrates a white light source, a blue filter and a yellow object. Blue filter All the colors Blue What color will the object appear? A yellow object illuminated by white light will absorb all the colors except yellow. A blue filter will filter all the colors except blue. Thus, when the blue light strikes the yellow object, it will be absorbed and the object will appear black (since it reflects no light). A) White B) Black C) Yellow D) Blue Click Click

Question-14 A green filter is placed between a red light source and an object. Red light source Green filter White object What color is the object? A) Red B) Green C) Yellow D) White E) Black A green filter will block (absorb) all colors except green. Since the light source gives off red light, the green filter will absorb the red light causing no light to fall on the object. Click Click

Question-15 Three different colored objects X, Y and Z, are illuminated by three projectors. Each projector emits a different colored light. The first projector causes object X to appear blue while the other objects appear black. The second projector causes objects X and Y to appear red while object Z appears black. The third projector causes objects X and Z to appear green while object Y appears black. What color do the objects appear if while light is used to illuminate the objects? White Red Green Object-X Object-Y Object-Z A) Blue Black Black B) Blue Red Green C) White Red Green D) White Black Red E) White Black Green X Y Z 1 2 3 Click

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